I think we need to keep in mind that many of these folks are either just starting out and/or have limitted availability of resources with the equipment they are using. Equipment can be extremely expensive. Then, you add in the cost of someone to do the filming, models, etc. It just gets cost prohibitive for the ordinary person to do all that's required to put out a quality product. Andre is right on the lighting issue too. (Good to see you around, Andre!)
I know that, when Drew and I did a few vids a while back, all we had was a single video camera...tape style. It took the film, but did nothing for quality or fancy edits. (We stated that fact right up front before anyone got to see more information on what we'd done.) Doing this purely for fun and for making things available to share with the community gave us a different perspective than those who honestly want to have a full-time business out of it.
I wouldn't be too hard on those who are just starting out...esp. if they've stated that this is a hobby and not meant to be professional quality. But, the concern you raise is yet another reason to check out preview clips that can show you the quality of the filming itself. If you don't like the quality, you don't buy things from them. Simple as that. If you're interested in the fun and don't care as much about quality, there's not a problem.
Bottom line... Those making material available for purchase should be up front about picture/sound quality. Those purchasing these materials should check things out before spending their money.
just my two cents...
Ann