I would have it checked out by a tech, AND I would plan a pool dive with it prior to any open water trips.
The BC holding air is only part of the story. I bought my BC used, and it held air just fine when I received it. However, when I used it in the pool, I found the inflator valve wasn't shutting off completely, and the BC would slowly inflate itself. While this isn't a major hazard if you're paying attention, it is an annoyance. Additionally, if the inflator is marginal, it is likely just a matter of time until it fails altogether. It wasn't an expensive fix, but if I hadn't used the BC in the pool, I would not have known until our OW dives in a remote location where getting it fixed would have been a problem.
We recently bought our regs from the LDS at their annual used gear sale, and arranged before our dive trip to try everything out in the pool. I don't know if all dive shops with pools work this way, but ours allows such check-out dives when the pool is not otherwise scheduled for classes, and for the cost of a tank rental ($5). Making sure everything not only worked right, but fit the way we wanted BEFORE another trip to a remote dive location only made sense. Having things fit correctly on land is a good start, but you also want to be sure the fit still feels right in the water.
As others have also said, you're trusting your life to this gear, and when it comes to your life, ignorance is not bliss. Getting it checked out is worth the cost.