I assemble new bikes at my LBS. Most bikes come with basic plastic platform pedals and all include at least a basic saddle. Both are required for a test ride, after all. For the few bikes that don't come with platforms in the box, we'll add a set from our stash.

I estimate that half of the customers upgrade the saddle, pedals, or both at the time of purchase. We give the customers a credit for the saddle (I don't know about the pedals), and add the returned ones to our stash.
If the customer wants to, they can buy a discounted saddle or basic pedals from our stash (some like to rummage), or of course we'll sell them a new saddle or pedals.

Obviously, the shop (or seller, if we're talking used bikes) should provide a saddle and pedals for a test ride. But I guess it's OK if the saddle and pedals are loaners, or price negotiable.