Based on your single experience with a used amp?I would not recommend the CMD 102P bass combo (similar component wise to the CMD 121P) due to past experiences. I purchased one used from a big box music store. Everything sounded great at the store but once at home the amp lasted about 20 minutes before it started hissing and popping and then I was unable to get any sound from the amp. Long story short I ended up bringing it back to the music store for a full refund and a sales associate candidly told me that they had 2 other units currently being assessed in the back room due to this same issue. Another thing to think about is the fact there seem to be very few Markbass service centres authorized to work on the amp should any issues arise. I believe the risk is too great in this case.

I've had the opposite experience,found the 6 new and used Markbass products i've owned over the last decade to be absolutely reliable. I bought a used Schroeder cab a month ago,that started having issues,and took it back for a full refund. (GC),but i'd never say avoid Schroeder products because of that.
Someone probably just didn't take very good care of your combo,or my cab.
It's always a crapshoot buying anything used....