Know the warning signs of gear failure and ask for shutter counts
1 3 4 5 6 7 8 9 10 11

Know the warning signs of gear failure and ask for shutter counts

This is in a similar vein to the previous tip: Always, ALWAYS research warning signs of failure for a piece of used gear you are considering purchasing. Some used gear holds up surprisingly well over time; some does not. For instance, early production Nikon 17-35mm F2.8 lenses suffer from the aforementioned failed focus motor. Knowing the warning signs of failure is essential. And don't be afraid to ask the buyer if 'the AF motor squeaks at all.' These kinds of questions and their answers can help protect you.

On a similar note, when purchasing a used DSLR, always ask for the shutter count. In the same way the odometer in a used car provides a metric for how much wear and tear it's received, so does a shutter count. Because shutters are only guaranteed so many actuations by the manufacturer - though many will pass their quoted shutter counts - it is crucial to check before you buy.