For me it would depend on the size and type of collection. If your time is flexible, the owner might suggest a time of day that the store is less busy so he can have more attention to give to pricing out a larger collection. If the collection isn't as large, stopping by might work ok. It certainly wouldn't hurt to give a call either way though.
If it is a good size collection, I would call first. You could just show up and if the timing is bad you may have to wait a while.
That wouls just depend on you. If its a huge collection yea. Give a call to give heads up. If its a small collection then just walk in and talk trade. The one that runs the place is looking only to make money from cards you trade.
Thanks! Your answer is awaiting moderation.