GeorgeTH - I agree with the first point - although even worse is the people that are using "private registration" services to hide their domain info - in most cases that I can think of, LLs and TGPs are starting to not accept those type of domains
On the second point - this is a case where a little more looking will probably help - there are people out there that use "virtual hosting" that could end up on an IP with 500 other domains - although the only way to verify that the other domains do not belong to the same person is to check the other domains (do a reverse IP to see all of the domains and check their whois) to verify that they do not belong to the same person - or Group
Its a little time consuming, but once its done it is shared (at least from what Ive seen within both TGP and LL communities) with others to let them know of certain groups trying to load a bunch of domains at once.
the third point - for a tgp at least - you could use
http://www.callpri.com/webmaster.html
to check a little easier - but if you feel uncomfortable with the submitter, its probably best to go to a msg board for that niche, most niches have some sort of gathering place for the tgp owners, and ask around - and of course - last resort - its your list