i think it all depends on a product you sell and on how big you are and also how good the second keyword fits it.
if you have like 10 products in your inventory then its definitely a shop. if your product is being made then its a shop (example: signshop vs signstore). if your product is related to any type of a grocery then its a store. shoestore sounds that it would have bigger selection vs shoeshop. but in same time shoeshop sounds that you can get something custom done with your shoe. but if the second keyword is more descriptive on what kind of things user is going to find then it depend on a sound (veganstore fits better than veganshop, but americanstore and americanshop both fit, but then you go back to the amounts and kind of products). cakestore sounds like a place to find a big selection of cakes. cakeshop sounds like a place where they actually make their cakes and you can have your custom one ordered. flowershop would be a place to order custom flower arrangements, while flowerstore sounds like more of a big slection of products available nationwide to deliver. hope this helps.
if you selling domains that would definitely be store unless you provide also full webdesign services and offer packages of the domain name/hosting/the site/full collateral/graphic design/ etc basically do something creative for your customer.