A forklift should be inspected properly and given a test run before buying it. This applies specifically to trucks being purchased online. It is important to detect possible issues with trucks acquired from businesses on-line.
Starting the engine from cold is a great idea. Note whether there is excessive smoke and the ease with which the engine turns over. This is especially vital with trucks which have IC engines.
The test run should include a check of the truck's performance in tough situations. A qualified operator can maneuver the truck in forward and reverse, up the ramp.
You can check an IC engine truck yourself. On a clear part of floor, run the truck around for several minutes while a skilled driver tests the hydraulic functions. Then, examine the ground underneath for indications of fluid leakage. Even seemingly minor leaking could result in serious issues which would be very expensive to fix later on.
A skilled person should check the chains and masts. Check with and without a load that the mast works smoothly. Watch for 'binding' or sticking of the mast. A warning indication is play in the mast channels or between the fork carriage and mast. Another is creeping forward or creeping down of the mast when loaded. These can be signs of problems with ram, valve or seals.
If the truck is not new, the mast may have been changed at some time. Make certain that the mast and any fitted attachments follow the rating plate on a truck. Check that the sideshift is not sticking when loaded.
Looking closely at the thickness of the heel for damage or wear must be included in the inspection. The truck's manufacturer specifies minimum thickness. A loose fit could mean the hanger points or carriage are worn. Watch for cracks on the arms at mountings and heels.