In my limited experience (been on the internet about a month), this is totally backwards. The 7-9s have all been exactly as advertised, it's the 5s and 6s who were actually 3-4s with clever angles and ancient pics. If there is no bikini or crop top in the pics, don't bother.
I feel bad for the real 5-6s, it's quite a lemon market out there for them.