I'm unsure about how this works. Are you creating surveys that get filled up by users? How is AI going to validate a business idea without input from real users?
Some more information about your process would help - because it sounds interested as a service but leaves a lot of questions unanswered.
Monetization is a bit tricky without making the userbase feel like we're selling out. I was more focused on making the user experience better before I think about monetization.
25% ownership doesnt appeal to me as much since I'd lose control over the direction and in that sense, I'd rather sell than work on it for someone else.
I'm not sure i want to sell but $50k is a decent chunk of money. I'm emotionally invested in the site but don't think about it as a revenue-generating business (or at least haven't so far)
Its something I built without much expectation and now there's thousands of people using it everyday. I get emails from them saying how much they love it. So in that sense, I really want to keep running it.
Given that, it might be instructive to get a handle on what the buy values at $50,000. Could just be the domain name and/or the "host authority" (when a lot of other (legitimate) sites refer to your site on the web it is perceived by search engines has having a bit more 'authority' than other sites.
If it's the latter you might find they buy it and replace your content with a bunch of links to porn web sites. You'd want to be ok with that before you sold it.
It's going to be pretty hard to estimate value without some idea of revenue potential. In the end, a valuation is going to come down to expected value: https://en.wikipedia.org/wiki/Discounted_cash_flow.
Apparently the buyer expects the value of your site to be >$50K for them. Question is, what's it worth to you?
Why not build a model of your revenues over the next couple of years in excel and calculate their sum?
Obviously a model can only tell you as much as it can accurately predict and you’ll probably want to generate some best case/worst case scenarios but then you’ll at least have a set of numbers to work from and know whether the offer is high or low compared to what you could make.
If there is no revenue, then the offer is likely a one-off opportunity. Don't expect a bunch of prospective buyers even if you hassle their CorpDev departments or potential decision makers.
$50K is likely a guesstimated amount, not based on some kind of calculations. It's basically "looks like it might be valuable, so let's give him some figure big enough for an independent developer but not too much".
Personally, I would haggle a bit (say, try to raise it $80K, then meet around $60K-$70K) and sell. Do not underestimate the uncertainty and the amount of money that needs to be poured to monetise the business. If it's coming from a small company or a person, they are more flexible.
Some more information about your process would help - because it sounds interested as a service but leaves a lot of questions unanswered.