I, too, don't mind losing to fellow collectors, but seeing resellers buying up stuff just pisses me right the hell off. The resellers have gotten pretty bad in my area, at least outside the 695 Beltway. Honestly, I think they're just afraid to come in the city, must be watching too much of The Wire. Ah well, more for me.
I'm in kind of a weird position with my yard selling, because I've got a number of goals I try to fulfill. First off, I love me some games, and in a way I *am* buying for my kids. I'm actively trying to build a library of the games I've loved over the years, so that when my son is old enough he'll get to enjoy them, too. He'll probably end up liking lacrosse or something though, but one can hope. I also leave my library open to friends and family, because what good is having these awesome games if I can't share them!? Additionally, if I'm out and see something friend needs for cheap I'll typically pick it up for them and give it to them for cost. I've become known in my friend circles as the guy who can get you weird/cheap stuff. (I bought the ugliest lamp the other day for a friend. It's like David the Gnome in Hell.)
I also go out trying to find stuff for the console area at MAGFest. This is where I get a little bit more cutthroat, because my budget there is crap since we don't have sponsors and don't charge huge badge fees (the higher-ups figure that people spend enough on the hotel). Last year I had about $4000 to play with, for a convention that ended up with an attendance of 12,000. With that money I had to buy new systems, flat screens, projectors, games, etc. Yard saling helps me stretch that budget out way more. When I'm buying for MAGFest I try to stick to $10-$15 for systems and $1-$2 per game, unless it's something we really, really need.
Lastly, I've also got to stay cost neutral, so I do pick a little bit up for reselling. I try not to take more than I need, but now that my wife and I have a baby and are saving up for a house, I have to be a bit more careful with my spending. It's unfortunate, but it's a choice I've made.
For the record, I do feel a little guilty about only paying $50 for that giant lot the other day. I knew it was way under, but the woman just wanted to get rid of it and was more than happy to take that much. She actually thought I was reseller at first since she said "I hope you make a bundle on it!" but I corrected her as to my true intentions. She seemed more pleased to know it was going to be enjoyed.
Phew, sorry for the whole confession. I'm probably going to spread that lot around a little bit, try to get some good karma racked back up. That Demon's Crest is definitely staying with me, though, no matter how many people I've got clamoring for it! (There are a lot.)