For my ads to be profitable I have roughly a 10% conversion from add to carts to purchase. 100 addtocarts, 10 purchases. I have a garbage store which does about 5% 100 addtocarts, 5 purchases. and that store is garbage and needs to be improved. Those ads still are revenue neutral though. 80 ads to 2 sales is low, but if you're just starting to advertise, it's not horrible. You need to make sure its obvious to the customer how to proceed to cart after adding an item to cart, then you need to make sure they're comfortable enough to complete the purchase. Additionally customers hate being surprised with extra fees, taxes/shipping, so perhaps eat those on your end so there's not a big shock in that increase. For me, say shipping costs me $8, I'll charge customer like $5 and eat the rest as a loss. Just test test test and increase that addtocarts to purchase conversion and you should be good to go.