Just holding holy water doesn’t necessarily mean an item is blessed (although typically fixtures for a Church will be blessed before use). That said, it is actually perfectly okay to buy blessed items, so long as you’re not paying more than what it is worth. If I have a rosary that cost $20 and I get it blessed, I can still sell it for $20. To sell it for more than what it’s worth would be to somehow imply that the blessing makes it worth more, or that I’m selling the blessing, which would be sinful. But there is no sin in simply buying religious goods–blessed or not–on the internet so long as your intention is not to buy or sell blessings themselves (which cannot be bought or sold).
-ACEGC