I apologize for my rant about the state our the nation and people's rights to sue.  I haven't ever been in that position (suing or being sued), but it just irks me to no end when I read about all the silly lawsuits that actually rule in favor of the person making the asinine claims.  It is most definitely true that courts are the only recourse for the wronged and history can definitely prove that (just ask people in colonial times or farther back)... I just think that it has grown beyond what it was meant to be.  I take issue with attorney's personally, being surrounded by them in my family. 

The fact is that if somebody is selling modules, as you state, they really SHOULD make sure they are good quality and they support them.  Unfortunately, they don't.  For every good developer out there, there has to be another 100 crappy ones.  I can't tell you how many people I went to school with that I thought were the biggest idiots and would never make it, yet they still graduated and got jobs.  The market is still such where a developer, good or bad, can get a job.  The last couple years had some rough patches and weeded out some of the crap, but there are still plenty of people out there that think "hey, I can do this... it can't be that hard" and then they put something out there. 

Honestly the only way I see to protect ourselves from crappy modules is forcing review programs at the main sites (DNN Marketplace and SnowCovered) -- DNN Marketplace has an optional one that gets you warm fuzzies and recognition, but because it costs money a lot of developers who are just barely entering can't afford to go through that process (whether they are good developers or not).  SnowCovered doesn't even offer that sort of review process and it is packed with crappy modules.

Me personally, and I know this is just me, but I would hate to have somebody purchase my product and end up not liking it or whatever.  I offer free trials for that very reason -- by all means, try it out and make sure it works for you before you commit to it.  I'd like to believe that when it comes to supporting my products and work I am a responsive person and try to resolve all issues.  Do I resolve every issue that comes my way?  Certainly not, some just can't be solved, but I definitely make an effort and exhaust all avenues before I give up.  Am I rare for a developer?  Probably, but not unique.  People like Mitchel Sellers, Ventrian, and others are pretty good about supporting their products, free or otherwise, and making sure people leave happy.  Perhaps it would be useful to build a site that reviews modules and developers, giving them grades and stuff?

I dunno... I do agree with your frustration though and again I apologize for my rant about the legal system.  It certainly isn't your fault the legal system has problems and that has nothing to do with DNN or anything else so it didn't belong in the post in the first place.

You say you are an attorney.  Well, I'm not.  However, I just have to point out:

• You say you are out $50 and you mention suing?  What attorney would consider this?  First off, even if your hourly rate is only $100/hr you are wasting your time.  Second, many jurisdictions will not allow attorney fees to be tacked on in cases like this (e.g. small claims level cases), so don't say your time will be reimbursed.
• You think you can make them travel to your city every month.  I'm no attorney and even I know you must sue a company in their place of business.  In other words, if I buy a module from a developer in CA and I'm in Florida and sue him, he would be sued in CA and I would have to travel, not him.
• Lastly, the software industry in the US has been afforded special protections from liability, etc.  Read any software license you have and it basically says buy at your own risk, this product may not work at all, etc.   Hey try this:  Go to a major retailer like Circuit City and buy any software they have.  Try it out then take it back and tell them it's crap.  See if you get a refund...you won't!  You expect more from random lone developers than from a $multi-billion company!

The bottom line:  Do what the other posters here said and RESEARCH FIRST.  Determine the top developers and only work with them.  Otherwise buy modules with source code and have your own programmer support them. 

I'm not a developer but please realize this: Many developers value their time at $40-$75/hour so if you buy a $50 module how much support do you really expect to get for free?  Be realistic in your expectations and you will be more prepared in this market.  Also be grateful that there are people willing to make free software like DNN and there are developers willing to spend time to make cheap modules.  Otherwise go buy a corporate CMS for $50,000 and expect to pay another $15,000/year for basic support.  Then you MAY be happy with what you get.

Now I will comment on your specific situation:

1. The developer that did not reply even though you bought 1 year of support:  First, realize the SLA on your support may allow him days to reply.  If more time than that has passed, then you are right.  This is not professional and you did not get what you paid for.  One tip is buy via Snowcovered where they post average time to reply to help tickets and allow you to post reviews.
2. "Another module developer will not refund my money even when he is aware that I cannot use his module as my website host prohibits use of his module. Therefore, he screwed me for 50 bucks. ":   No he didn't.  Why is it the developer's fault you didn't research whether your host supports the module 1st?  That's your responsibility, not his.
3. "In addition, one module developer told me that some of his modules are not supported, which he does not mention anywhere on his website. WTF?":  He should mention it but you should also ask prior to purchase.  Many major software vendors do not include support for their products, including big ones like Microsoft.  Many will charge you by the minute if you call them.  Not unusual.