Its either a 2018 iPad Pro or a 2020 iPad Pro, so it is definitely a good deal.Without further details about the iPad model, condition (i.e. new/used) and seller (dealer/private) it’s difficult to judge.
My advice is don't buy based on price only, and consider the other factors too. Is it new? Is it used? How used is it? Is it refurbished? Who refurbished it? Where are you buying it from? Is there a warranty? What's the return policy?
Yeah, 1TB ipads pro 11 2018 sell for over $800 even in not so great conditions, so at $600 something seems wrong... maybe the battery doesn't hold a charge for long or some other issue... make sure you at least see actual picturesWhy is the price so low? Is there an underlying flaw, is the seller desperate for cash, was it merely gifted to them and they don’t need it or is it stolen?
Those questions come to mind for me first before getting to the others (which are good btw).
A quick look at swappa shows that this price is unusually low (not that there are 1TB versions currently listed but its a given that any 1TB will be valued higher than 256gb or 512gb versions).