I bought my Medisoft off Craigslist and didn't have any problems but it was brand new, unopened, etc. but I agree, you can't just buy the first one that comes along. Programs like Medisoft aren't terribly expensive to begin with and if you're the only one using it you can get a single user version for a reasonable rate. Microwize is the company I've bought through quite a few times when I've done consulting and they were willing to beat any quote we were given by 10%. So that's something you might want to look into as there are no additional charges once you get the software.
Modalities, like stim, ultrasound, manual therapy, etc. can increase the reimbursement per claim by over 100%. I've worked for a Chiro that billed out there ex, manual therapy, nuero muscular re-ed, traction, stim, etc. and his billed amount per claim, on average was 500% more than that of a chiro I worked for who did nothing but $45 adjustments.
Alot of Chiro's discount their services, especially where out of network claims are concerned. They don't want to go in network and take the huge discount but they also don't want to hold the patient responsible for the additional fees. They see it as a win-win scenario.