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Bought most of my gear used (within a local 100 mile radius), with no
significant problems. There's a lot of good gear out there.

Try local first so you can examine the gear personally. Dive shop
bulletin boards sometimes have good items. Dive club members. You might
get some tips from the instructor, unless he's beholden to the dive
shop.

Some dive shops sell old rental gear at substantial savings.

Bargain papers usually have a bunch of good gear, especially if you're
near heavily dived areas.

EBay, if you're savvy about what gear you want and can judge which
listings have gear you feel has been well-maintained, which is not
always easy to do. Gear personally owned by the seller is a plus. Make
sure they have an excellent eBay reputation (substantial number and
percentage of positive feedback, such as 100 or more and 99% positive).

HTH.

Dave C

Rent first.  No need to make an investment until he knows he'll like
the sport.  He'll lose good money selling it on eBay.

If he rents, he gets to try out the gear until he finds something he
likes.  Many shops turn over their rental gear pretty regularly and he
might find stuff he wants at a good price.

Find a local dive shop, make friends with the owners and staff and
they should show him the various brands and options.  If they don't,
find a shop that will, after all, he'll eventually be a customer.