I'm not sure if it's a 10 or 10A? The picture he posted only shows the front and I can't tell what spkr(s) it has? I'm gonna go over to his shop and have a look see. I will update later today or tomorrow.
The M10 has three control knobs per channel (vol,tone,contour switch), the M10A has four control knobs (vol,treb,bass,contour switch). Both have 2 vib. knobs, 1 reverb, and 1 power switch. So M10=10 knobs, M10A=12 knobs. Note that the M10 knobs are all in a single row, the M10A has a little diamond layout for each channel. See the pics on those site and it'll ring clear.
Also, the M10 has a gold motif (faceplate and grille-cloth, although the grille-cloth can be faded to a wheat like color), and M10A is usually, if not always, silver.
If you go check it out, bring an assortment of allen wrenches with you. there are two allen head screws on either side of the top. remove these and you can 'open the hood' revealing tubes, and circuit. on the circuit side, make sure the little circuit board isn't broken, and there should be a good assortment of caps including ceramics, chiefs, and blue molded caps Iif all the 'nice' caps have been replaced with cheap yellow mallory 150's, watch out. on the tube side, the original 7189As were GEs. make sure someone didn't just stick EL84s in it. all the preamp tubes are mullard (and maybe some GE or RCAs), and might have "Estey" screened on them.