I don't think it is a question of wanting to sell nikon or cannon over pentax, or lack of knowledge.
I can go into any of the large camera stores in toronto, walk up to the pentax section and have a discussion with them on pentax cameras, what I shoot, what lenses I am looking for etc. and get good advise when I am looking for new equipment.
Maybe I'm lucky or maybe the same guy works in all of them!
but I think the difference is, many stores will promote the 2 big names over all others because they have stock. The success of pentax over the last couple of years has made things scarce, and the market hasn't sorted itself out yet.