At this time of the year, any fruit tree still alive at a home improvement or box store is one tough customer, and if an appropriate choice for your area, at 40% off, I'd snap it up in a heartbeat!!

What you are seeing on the foliage is not a disease - it is just normal wear and tear that one would expect with a tree at that sort of retail outlet and some typical seasonal deterioration.

As long as you don't mind that it may not be what the label says. Mislabeling is rather common for trees from big box stores. Also, before you plant loosen up its rootball. Trees in pots can get root bound and could be stunted or dead if the condition is severe and not corrected.

You're in the Northern Hemisphere, right? Apple trees normally lose their leaves this time of year! Looks like a great deal. I would get it. Actually maybe I should go shopping and look for deals like this, as one of my own trees just died (terrible unreversible fireblight) so it was ripped out and I need to replace it.