Not to be a smart a.s but "ebay" doesn't sell transmissions.  They are
just a conduit for someone else to sell you a product.  The process is
always pretty much the same but the quality and service is going to
depend on the person selling you the transmission.  Check the sellers
feedback closely and check auctions from multiple sellers to make sure
the prices are in line.  Watch out for shipping prices!!!  That seems
to be the latest trick on e-bay..  sell you an item for a low low
price and then charge out the kazoo for shipping.  E-bay only charges
the seller  a percentage of the selling price so it is an easy way to
cheat the system.

Personally if it was me I wouldn't buy a transmission from e-bay.  The
shipping expenses would surely take a big bite out of your savings.
E-Bay sellers can be kind of hard to find again if you have an issue.
If that transmission craps out in a month will you still be able to
find them for service?

          Steve B.

What I would do is go to a reputable mechanic you trust locally.  At least
if something goes wrong, you can go back to someone and they can redo it if
necessary.

My '92 NX 2000 needed a rebuilt tranny a few years ago, my local mechanic
knew of a good rebuilder and sent the car off...it came back, but he didn't
like the way it shifted, so he did all the chasing down for me, and gave me
a loaner car in the meanwhile.

He said that they ended up using my old transmission with virtually all new
parts inside...his pestering carried much more weight than if I had've been
bugging them because he threatened to stop sending any more business their
way, whereas as an individual, they can just shrug you off.

With E-bay, it's definitely buyer beware...