On a semirelated subject, I remember the first 2 seasons of Ghost Hunters, where they aired EVERY case they did - whether they "found" anything or not. This, while boring at times, gave light to the fact that not every case gets positive results, or even spectacular results. Nowadays, it seems that SyFy only broadcasts the sponsored cases that definitely have major "paranormal" discoveries; GH doesn't even seem to do private residences anymore. It's a shame, I used to like the show, now I think I prefer Haunted Collector... John Zaffis and his crew take a much more realistic and professional approach to what they do.
In regards to reality shows like Pawn Stars, the reason they only show the expensive stuff is this: when you watched Antiques Roadshow, did you really care about the people who brought in cheap junk to be appraised? No, you didn't. The exotic, rare, and unique stuff always sells. Plus, I'm sure they get people who bring in multiples from time to time, of swords and guns and cars and toys and Coke products and I could go on, and on, and on... too much stuff to put into one season, much less one episode...
So in conclusion, of course MD shows are going to highlight the best finds and downplay the small stuff. No one wants to see some guy out in a field raking in wheat cents and common silver dimes. I think I would only watch a show like that if it were a local area, or the guy was professional and knowledgeable and frequently gave tips or used different MDs in different locations, or did joint hunts with show fans. The profit part doesn't bother me a bit, except where locally-significant relics may be concerned. Other than that, I'd definitely watch an MD show bc I'd be taking notes! And before anyone can say it, I do have enough common sense to know what NOT to write down!