Here are some things to check for:
1. Check the girl's name, phone number or email in TER to see if she has reviews. This is the best way. If you want to get into this hobby, pay the $20 to get a VIP account at TER even if it's just for one month. It's worth it IMO.
2. Google the girl's phone number and email from the ad and see if there are hits on any forum about her being a scam or if the number is associated with any scam.
3. Reverse search the girl's photos from the add at Google image search and also
https://yandex.com/images/search. Do both because sometimes one misses and the other catches it. Most of the fake photo users are very obvious but sometimes they're really savvy and use some obscure IG or OF girl's pictures with watermarks cropped out. I need to point out that two of the hottest women I ever saw used fake photos, but that's pretty rare. Most legit escorts just use their own photos and blur their face.
4. Scammers know that you can't discuss escorting on OF, so they use a real OF girl's photos and link to her OF to make their ad look legit because they know it's nearly impossible for you to confirm they're fakes.
5. If it looks too good to be true, it is. A hot 8 or 9 girl isn't fucking for $400.00 in the U.S. You can find blazing hot girls for real in other countries at those rates and Canada in particular has some hot escorts for less than they'd charge in the U.S..
6. This is a little more involved, but it's kind of fun anyway. Use a free text app like Textfree to get a burner number. Text the girl a few questions saying you want to see her. If she starts asking for deposit now, tell her you can't until you get paid in x number of days. A real escort will stop responding, respond "ok let me know when you're ready" or tell you to fuck off and block you. Scammers are so hungry that she'll keep responding and reminding you for days.
7. Not every ad requiring deposit is a scam, but many are. My rule of thumb is if the girl has no reviews on TER I'm not paying a deposit. If the girl is well established, I'll pay the deposit. I've paid deposits for two girls but they were both well known with active Twitter presence and personal websites and each had dozens of rave reviews on TER, plus they were incall sessions so they needed to book a hotel room, which came out of the deposit.
8. Also, this isn't to spot scammers, but check their social media if they have it and observe the vibe. Some escorts hate what they do and clearly loath men. When most of their posts are complaining about clients or making fun of them I block them. This helps if I forget down the line, find this hot girl and go to check her Twitter and see I blocked her, that tells me there was a good reason for it, so I don't book those. I learned early on that the negative, misandrist escorts will be just as bitchy and unpleasant towards you even if you have the best attitude possible.
The problem with what you're asking for is that Tryst and Private Delights are where most escorts advertise. Eros is "better looking," but too many of the ads there are scams and too few of the top legit girls advertise there. I think PD is a tad better and the outright scammers and thieves will get negative reviews at least, but in smaller markets (mid sized cities and smaller) you'll find more ads on Tryst than PD.
I get that Tryst and PD look shitty, but they're advertising illegal services, so they don't have a lot of motivation to make better looking sites. Hell, OF is legal and rich as fuck and look how lousy that site looks and works.