On Harv's island and aboard the Treasure Trawler, you can only buy one piece of art daily. Overnight, Redd will package up the piece and post it to you for the next day. I find this incredibly frustrating, and it’s taken me such a long time to flesh out the content of my museum because of it. If you could buy more than one piece of art daily, I think it would hugely lessen the odds of buying a fake. So maybe it’s just a ploy to get Redd more money!