I wouldn't. It's either already failed and hopefully whatever failed has been replaced which could mean it will fail again or it's been returned for some unknown reason and has most likely just been checked that it's working and put back into it's box for resale ready for the next unlucky customer to be unhappy with it. Refurbs/B-Grade typically come with a much shorter warranty while only have a small amount taken off the sale price. Some sellers idea of refurbishing something is making sure it's all there and sticking it back into it's box so you can't be sure in any way that it's been done to the standards that you expect.
There are several things I wouldn't buy as a refurb/B-grade and that includes AIO's, PSU's, storage drives and memory.