It's a can of worms isn't it. Even if you did catch what you thought was a good brand and there was only one individual/company using it, you have to ask yourself what is better for them? Is it better to stick it on Sedo, wait for a different buyer to come along, build their business on it and the other party be none the wiser that the domain was even for sale? I think not. As Edwin said, the more people using it the more generic it becomes and therefore ultimately more difficult to win a DRS case over it. Couple that with the brand being so generic that it could be used by anyone in any sector, I can't possibly see how it would be deemed abusive.
Ironically the only domains I've ever lost via legal means have been what we know as generics.
If I see what I think is a good domain in the drop list, even if only one person is using it to form their brand, I'd catch it. The difference is it wouldn't be caught for the intention of selling to them and I certainly wouldn't be e-mailing a single buyer with an auction link. As I say, several people though, fair game.