Built to handle rough terrain, second hand full suspension mountain bikes are perfect ride-anywhere all terrain bikes. With front and rear suspension they soak up the bumps offering the rider greater control and comfort over rugged terrain. The amount of suspension, or travel as its called varies considerably depending upon the intended use; cross-country (XC) racing, Downhill, Enduro or freeride. Full suspension mountain bikes tend to be the top of the mountain bike range, with complicated pivots and shocks there is a lot going on, but to ride they are fast and forgiving.

Check the travel: Make sure the suspension travel matches the specifications of the bike's model. You can find this information on the bike's manufacturer's website.

Inspect the shocks and forks: Check for any leaks or damage to the shocks and forks. Make sure the adjusters and rebound knobs move smoothly and are not seized.

Check for play: With the bike on a stand or held off the ground, push and pull on the bike to check for any play in the suspension linkage. Any excessive play could indicate worn or damaged bearings, which can be expensive to replace.

Check the sag: Set the sag correctly for your weight and riding style. Check that the sag is consistent and doesn't change when you sit on the bike.

Rebound and compression: Check the rebound and compression damping settings. Make sure they are adjusted correctly and function properly. Too little damping will cause the bike to bottom out, while too much damping will make the ride too harsh.

Check for wear: Look for any signs of wear on the suspension components, such as the seals, bushings, and o-rings. These parts can wear out over time and may need to be replaced.

Have it serviced: If you're not confident in inspecting the suspension yourself, take it to a professional bike mechanic for a full service. They will be able to give you a better idea of the condition of the bike and any potential issues.