Many times 🙂 Aside from plain false advertising, my pet hate (and something that is not often detectable from a preview clip) is when a clip is poorly spliced together and full of edits...
An occasional cut I don't mind; sometimes there are legit reasons to place cuts in a clip - trimming excess footage, scene changes etc. I'm talking about "cover up" editing to hide that the model is getting sneaky breaks every 30 seconds, or poorly tied bondage undid itself, or the phone rang and they couldn't be bothered to start the scene again, or the guy holding the camera started talking/prompting the 'lee and broke the flow of what was going on - the kind of things that are completely avoidable if you care. Potentially great clips can be completely cocked up with poor filming / lazy editing, but you'd never know from the screencaps and preview. I know there's not some great tickle clip conspiracy, but it's hard to feel any other way than disappointed and that someone is selling you shoddy goods when the flow of the clip keeps breaking 😛
I'd guess it's about 50/50, but many producers seem pretty averse, or just plain hostile towards even the most contructive criticism (to be honest, many seem more interested in topic bumping by moving straight on to the next "great clip!" comment rather than actually conversing) which is why I tend to just not buy from them again, or run a 3-strike rule if I'm not happy with the quality of the clip.
Anyway, thankfully there's always a good selection of producers that take the effort to produce quality clips ...so it's not the end of the world 🙂