I am buying a used Aptus 17 digital back and I will have an opportunity to test it before paying for it. Obviously, I will take some images and make sure it can capture an image.

Other than that, what should I do to test the back?

Ask the seller for the serial number of the back, then contact your local distributor or the dealer whom it was bought from to find out if it is still under warranty.
You can check the frame counter, which is at the bottom of the "Setup" menu (under "About".

Also look for any scratches on the IR filter and make sure that the fans are running quietly.

Try it with a CF card and also tethered (you can download the latest LC11 from our website)

Last, look for any missing accessories. In general you should have a 4.5m FW400 cable, 2 batteries, 1 charger, a Grey card and then a sync lead and a focusing screen, depending on the mount that the back is in.

Good luck

Yair

It also comes (in general) with a white plexi and a case for the back itself doesn't it?

(Greetings everybody, I've been lurking for some time, this is my first post.)

Roger, I don't know if this is important to you or not, but for me, the first thing I tried was a dust shot - defocus the lens to nearest focus, set the aperture to f/22 (or smaller), shoot the sky. It will give you an idea of whether the IR filter is very dirty (or clean), or if there are any other sorts of marks that might be visible only when shooting stopped down. If just gives you at the very least an idea if you will need to get the sensor cleaned as soon as you get it. I would say it's unlikely, but it may also help to reveal microscopic marks. You don't want to come away from it thinking that everything is hunky dory only to find this out later just because you didn't think of trying it...

Jason (Ixpress V96C)

2 batteries? My Aptus unit from Leaf only came with 1 battery? Did I get ripped on this also?