so if the NPC shop doesn't have the item I need, or if it's more expensive than in the usershops, I go by the block of lowest prices (usually about a dozen matching prices) and then to: does this person have more than one of this item? from there it's the better shop name
(for the record: my 'everything goes in here' shop is DryadGurrl's Discount Grocery and my holiday ornament shop is DryadGurrl's Decor Galore in keeping with the theme)
BUT ALSO: it can depend on the item I'm buying, if it's a battle/armor item, I'm more likely to buy from 'Armor & Stuff' than I am from 'Junk Bin' and if it's a book, 'Los Bibliotheque' is going to win out over 'giveaway fund!'
from there it's the better shop name