I cant' think of one that would combine the "drop off" feature with the invoicing. You might be able to modify an existing template to add that with out too much difficulty by adding a new table or two with layouts to support them. (Why would a customer drop off an item at a retail store? Dry cleaning?, Consignment sales? Dogs that need grooming?....)
consignment. any suggestions?
Consignment means you'll need to track a lot more data on those "dropped off" items than for some businesses. You'll want to track not only who brought in an item, when and for how much it sold, but you'll want to link it to a sales invoice where it is sold and also the amount paid to the seller once it sells.
In many ways, this is a purchase order and invoicing system. The purchase order is started when an item is brought in and the "vendor" is your selling customer. The invoice logs when it is sold to your buying customer. There are a number of templates, two come with Filemaker as starter solutions (purchase orders and invoices) and there's also a business productivity pack you can take a look at, but I suspect that it would need at least some customization to fully fit the business practices of a consignment shop.