I have tried many (Working Artist (faaaar too complicated), ArtLook (good, just didn't have featured I wanted at the time), ArtButler (rubbish, bad design, hard to figure out and help file isn't helpful, and their site is down it seems), my own Filemaker design) and just found Flick which I LOVE. It's for the business side - inventory, customer lists, gallery/show tracking, you could put in prospects because you can add 'customers' before linking them to any actual sales, it does a few different print outputs of image + info of your choice that I'll be using for gallery sheets, receipts or CoAs (printing onto my own 'letterhead' or template). I'm banging the drum about it a bit much this week.
Anyway, you can see a free trial from their website. http://www.arawak.com.au/
I think all levels can get to grips with it, beginners might need a bit more time as they would with any database-built software though. It's very visual (very Mac looking, though it is Mac and PC) and clicking buttons to see what it does won't blow anything up.
It may not do everything (no accounting/bookkeeping) but what it does it seems to do more straightforwardly than the others I've looked at - without the clutter of trying to include too much (like Working Artist).
There may have been other mentioned in the Art Business forum, it comes up somewhat regularly.