I like to buy from a local reputable dealer....but that is not an option in my area, unfortunately. My K5 came from B&H, a fine and respected online dealer. I have also had good fortune with Adorama, and would not hesitate to do business with them at any time...and surely will in the future.
Prodigital....never used them but have heard generally positive reports.
Steer clear of sites "too good to be true"....they are.
Best Regards.... and if you are not excited about getting the K5, you should be! You are in for a real treat! It carries the Otis Seal of Approval and Satisfaction Guarantee.....it doesn't get any better than that!