In theory, there could be “fake customers” among them in the sense of other sellers trying to get information out of you, but it’s much more probable that it’s just people who “window-shop around” and go with someone who offers cheaper or faster work, or they prefer to work with for whatever other reason, or they might decide to do it themselves and not buy from anyone in the end in some cases, or it might be hopeful resellers who are looking for the least to pay for the highest margin.
You can set up some quick responses if you end up typing (almost) the same things regarding their questions, then you’ll waste less time.
Reporting people only makes sense if they somehow violate Fiverr’s terms of service.
Regarding the response rate/time, here’s the FAQ: https://www.fiverr.com/support/articles/360010452637-Response-Time--Rate-FAQ
However, I guess nobody is completely sure if it still applies after the recent changes, as afarigh said. Maybe we’ll hear from someone who’ll ask support about it if their rate seems to suffer because of that.