Most online stores give you a box to click when you place the order: Is this a gift? [ ]yes [ ] no. If you click [x] yes, you get another box where you can write a short message to the recipient. Such as, "Happy Birthday Susan, Love, Bob & Jane." And they automatically include a gift receipt without the price, instead of a normal receipt.
It's kind of expected for larger online retail businesses to do that, since so many people buy their gifts for long-distance friends & relatives online.
I know we like to think we're special because we're selling art... but to someone looking for gifts, we're just another place to get a nice gift for Susan online. They expect the same level of service as the places that sell pink fuzzy slippers with bunny ears or lego kits.