Show them the prints without the frames, although in this case it might be best to have one framed--a duplicate of a print you are showing them-- as an example of framing. Use Nielsen metal-section frames. Inexpensive. We use "Contrast Gray" #11, although I still like the extraordinarily conventional slver (#11). White frames are also nice. Black frames can be elegant, too, but they can easily overpower the work. The number refers to the design of the frame. Number 11s are the "standard" Nielsen frame. Number 33s have an elegant narrower face and are particularly suitable for smaller works.
In back of the mount, you will need an acid-free backing board. Do not use the spring clips that come with the hardware. They are awful. They rust and they make for wavy mounts. Instead, a piece of mat board behind the frame fills the space. If there is a little more space left, cut 1" strips of mat board and use them as spacers.
There is so much more I could say about frames, but time is short and this should give you a start.
Michael A. Smith