Welcome to the forum.
First, he
IS a salesman and I think it's probably safe to say that his store doesn't sell Pentax. If they do, they probably don't actively push Pentax.
It seems like you've done a fair amount of research already and I'm sure your previous photographic experience will help you come to a decision you are happy with. Whichever system you decide on is going to be good quality.
In lens stabilisation supposedly works better for longer lenses. Another advantage is that you can actually see it working through the VF as you focus. In camera stabilisation is an act of faith as you can't see it working. You pay a premium price for in lens stabilisation. With in camera stabilisation it works with any lens and in the case of Pentax, it'll work with forty year old lenses that you can pick up for a few bucks at a thrift store.
Pentax probably has the best value for money.
Pentax are also renowned for lens quality, that's something no self respecting Canon or Nikon owner will deny. In fact many of them use the old Pentax lenses on their cameras with the aid of adapters or modifications.
I hope this has helped and good luck with your decision making.
I'll leave you with a plug; with Pentax, you also get this forum.