As it's second-hand, can you find out from the seller whether it still has the MFX protocol active, or whether that has been disabled? Is it coming from a dealer or direct from the previous owner?
MFX decoders with all options active (ie: as supplied) will always look for an MFX command set first, then if they don't find one they will then look for DCC - however if you're never going to want to run it on an MFX system then it is usually worth deactivating that protocol so that it goes straight to DCC and doesn't get confused...
There are some other things (and how to do them) that folks more expert than I will hopefully chip in with!
Jon.
PS: what's the loco?