I've had a few great sales on Flippa, and I've made a couple of good purchases as well. Times have changed though. Flippa hasn't been the same since they went in a new direction a couple of years ago. It's become a lot more about eCommerce businesses/apps and the revenue that comes with them. That's understandable, but you have lots of these people listing websites for sale claiming that they generate hundreds of dollars in ad revenue. I'd say a legitimate asking price for those types of sites would be 2-3 years worth of revenue. If they're selling a website for a fraction of what they claim to be generating, I'd say it's safe to say that it's too good to be true.
You'll also notice that a lot of these types of listings are websites that are starter sites that are only a few months old. So sure, maybe they've generated a few hundred dollars each month since starting up, but that's a sketchy situation to get involved with. If you're buying a website as an investment, wouldn't you like to see a proven track record of consistent revenue? These types of websites typically have less than legitimate methods to generating that revenue, such as blackhat techniques, for example. I'd also be weary of listings that list ad revenue being generated outside of Adsense. Obviously there's tons of legitimate ad platforms besides Adsense, but if someone is claiming to generate $xxx on a monthly basis and they're doing it through an ad marketplace that you've never heard of, how can you be certain that they also don't own the ad marketplace itself? If they did, they could very well just be making fake sales to themselves within their own ad platform.
The bottom line is that there's lots of ways to get scammed, and it doesn't matter whether the sale is occurring on Flippa, Digital Point, FP, TAZ, etc. As far as the company itself, you can trust Flippa. But don't ever assume that every individual listing their web assets for sale are doing so with good intentions. You can get scammed anywhere. Be cautious, and do your due diligence.
