Jay - knowing who you are talking about and having had our small conversations about the same problem, I know how ya feel - as do a lot of webmasters here. I guess that the best solution in my mind to this is a little less on the harsh side, but it's something I learned real fast from being hard-headed when I first came into the biz.
First off - helping new WMs when they are stuck or just can't figure something out by reading the posts here or at any resources we recommend a lot around here is, to me, an exchange that should take place, for two reasons. One - it helps us as LL, TGP whatever owners to get people on track for their submits and make money for all involved. Two - that new WM may be the person you would like to trade with in the future and they will remember the help you gave - most of the time.
That brings in the second part - when you start seeing one WM sticking out as someone who exploits everyone and screws you without even a "thanks" - it's time to at the very least, make people that you know trade or do biz with that person aware of whats going on - just like you did in this case - and I'm pretty sure the whole network of people that do trades with that individual will look a little harder at their biz with that person - in my case, when I found out about a particular WM, I shared that info through a few icq contacts and emails. That WM no longer has trades with a lot of people.
Last - I've been looking back at a lot of info that I've put out in articles, posts and irc chats, and in most cases I found that most of the info I was sharing was info that was available through a quick search of many boards and SE info sites. My stance, although I fall into the trap of blabbing too much sometimes, is to now answer requests for info by pointing people towards certain resources, and to let them get out of that reading what they will. I've talked to other WMs about the exact same thing you're going through and they have also taken this approach.
It sucks to give out a lot of info that is helpful, to just have it thrown back at you in the form of competition and thanklessness - At the same time, I know if it hadn't been for a few people that are now running this board and mods here, I'd still be hardheaded and probably working at a plant somewhere
but I do let them know through the trades, traffic and thanks as well as biz I throw at them because of that help. Like my momma always said - what goes around comes around (deep southern drawl on that one)