It is standard practice to sell the horse with no tack. However, I will usually send hard to fit items, like hoof boots and possibly blankets, with the horse. I let my previous mare's hoof boots, joint supplements, a nylon halter, and a half bag of feed go with her. I almost sent her blankets, too, but they were so expensive and I was hoping to trade them for the right size for the new horse. If the new owner had asked to buy them, I would have given her a good deal, though. Same on pretty much anything else I bought specifically for the mare.
Tug on anything at all and you'll find it connected to everything else in the universe.~John Muir