It's actually against the rules to ask someone to buy from your shop, as it is considered "begging".

There is an alternative though.
If you put a junk item into your shop for 1 MP, Scrooge will take it and you'll be able to empty your shop til about 1 minute after you've priced the item for sale.
I use pies from Pie Throw personally.

Very helpful on quests!!!!