Which tool to choose
You don't need subscriptions. Choose based on what you're buying.
If you're buying something standard (an appliance, a smartphone, a used car from a dealer), use free ChatGPT. The free plan lets you search the web, analyze data, and upload images or files. That's enough to build the list of questions and check the seller's answers on the spot.
If you're buying something that requires in-depth research (a house, an investment, an expensive piece of machinery where every detail matters), use Gemini with Deep Research. Google has made Deep Research available to all users, without an Advanced subscription. It's a tool that does the web research for you and saves you the page-by-page hunt for useful information. It's good when you need to compare models, market prices and real reviews before you even talk to the seller.
The free plan has a limit. On free ChatGPT you can send up to 10 messages with the full model every 5 hours, then the chat switches to the mini version until it resets. To prepare a list of questions that's more than enough: you'll work in a single session.
How to do it
From a browser or from the app the path is the same:
- Open ChatGPT (chatgpt.com) or the Gemini app and start a new conversation.
- Paste the prompt below, replacing only the three initial pieces of information (item, budget, context).
- Read the generated questions and ask the AI to dig deeper into the areas that worry you most ("give me 5 more questions just about the warranty").
- Save the list: copy it into your phone's notes or print it.
The operational syntax:
I'm about to buy: an 8 kg washing machine, mid-range.
Maximum budget: 600 euros.
Context: I'll use it every day for a family of four, replacing an old one that broke.
Act as an expert, skeptical purchasing consultant who has already seen every seller's trick.
Generate me a list of 15-20 precise questions to ask the seller before signing or paying.
Organize them into four blocks: price and hidden costs, real quality and performance, warranty and support, delivery and installation.
For each question, add in parentheses why it matters and which answer should make me suspicious.
Use simple language, as if I had to read them out loud in the store.
Check the result: if the questions are generic ("is it good quality?") the prompt didn't work. They must be specific and verifiable ("is the declared energy class confirmed on the EU label of the product in stock?"). If they stay vague, reply to the AI:
These questions are too generic. Make them concrete and verifiable on the spot, with details I can check by eye or ask to see.
For preliminary research, on free ChatGPT you can take advantage of web browsing with source citation. Add to the prompt "search online for the average market price of this model and tell me the sources" to get a number you can bargain with.
Concrete example
Marco needs to buy a used car, a six-year-old compact, budget 9,000 euros. Instead of showing up at the seller unprepared, he pastes the prompt adapted to the car. ChatGPT gives him back questions like: "Can you show me the complete service history with the workshop's stamps?", "Has the timing belt been replaced, and when?", "Can I take it to my own trusted mechanic before buying?".
At the dealership Marco reads the list off his phone. At the question about the timing belt the seller hesitates and says "it should be fine". That "should" is the warning sign the AI had flagged in parentheses. Marco asks for written confirmation, discovers the belt has never been changed (a 600-euro job) and uses the fact to knock 500 euros off the price. The list cost him zero euros and ten minutes.
When it does NOT work (and how to fix it)
If the AI makes up prices or technical data
Models can produce plausible but false numbers. Don't trust the prices or specs the AI cites "from memory". Always ask "search for this information online and give me the link to the source". On free ChatGPT web search is active and cites sources: open the links and check the data yourself before using it to bargain.
If the questions stay too generic
It means you gave little context. The more details you provide (real use, what you're switching from, what disappointed you in the past), the sharper the questions become. Add a sentence like "my last washing machine always broke because of the drum bearings" and the AI will generate questions targeted at that weak point.
If you've run out of free messages
After 10 messages every 5 hours the chat switches to the mini model, which is weaker. To prepare the questions the mini holds up fine anyway. If you want to continue with the full model, open Gemini, which has different limits: paste in the list you've already made and ask it to improve it, so you don't start from scratch.
If you have to compare several products and get lost
A simple chat struggles with elaborate comparisons. Use Gemini's Deep Research (free): ask for a comparison of three specific models with prices, pros and cons and sources. It gives you back a structured report you can reread before buying.
A tip from someone who actually uses it
Don't just generate the questions: have the AI play the seller. After receiving the list, write "now pretend to be the seller who wants to close fast, I'll ask you the questions and you answer evasively like he would". You train yourself to recognize wishy-washy answers live and you arrive at the store without being caught off guard. It's the difference between having a cheat sheet and having already done a dress rehearsal.
Frequently asked questions
Do I really have to pay for a subscription to do this?
No. The free version of ChatGPT or Gemini is enough to generate and refine the questions. The free plan today includes a recent model, web browsing with source citation and file uploads: features that until a year ago were paid-only.
Can I have the AI read the contract or quote the seller gave me?
Yes, and it's one of the best uses. The free plan accepts images and files: photograph the quote or upload the PDF and ask "read this document and list the clauses that are unfavorable to me and what I should ask to change". Don't upload sensitive personal data (tax code, IBAN): black it out first.
Does it also work for buying services, not just products?
Yes. You only change the item in the prompt: "an electricity and gas supply contract", "a loan", "an annual gym membership". The four categories (hidden costs, real performance, lock-ins and cancellation, terms of provision) adapt to almost anything.
Don't I risk seeming fussy or rude by asking the seller twenty questions?
That's the fear that paralyzes people who spend thousands of euros and then discover the surprises afterwards. A serious seller appreciates a prepared customer and answers without a problem; someone who gets nervous in front of precise questions is giving you the most useful signal of all. The questions aren't there to start an argument, they're there to surface what you'd otherwise discover too late. You don't have to ask them all: keep the list as a safety net and use the ones that matter for your case.