A forklift should be inspected well and given a test run before buying it. This applies especially to trucks being purchased on line. It is really essential to detect possible issues with trucks obtained from businesses on-line.
Starting the engine from cold is a good idea. Note whether there is excessive smoke and the ease with which the engine turns over. This is especially crucial with trucks that have IC engines.
The test run should include an inspection of the truck's performance in tough situations. An operator who is trained can drive the truck in forward and reverse, up the ramp.
You can inspect an IC engine truck yourself. On a clear area of floor, run the truck around for several minutes while a skilled driver tests the hydraulic functions. Then, look at the ground underneath for indications of fluid leakage. Even seemingly minor leaking could indicate serious problems which would be costly to fix later on.
The masts and chains should be checked by a qualified individual. Check with and without a load that the mast operates well. Watch for sticking or 'binding' of the mast. A warning sign is play in the mast channels or between the mast and fork carriage. Another is creeping down or creeping forward of the mast when loaded. These can be signs of issues with ram, valve or seals.
If the truck is not new, the mast may have been changed at some time. Make sure that the mast and any fitted attachments follow the rating plate on a truck. Check that the sideshift is not sticking when loaded.
When inspecting the forks, look closely at the heel thickness for damage or wear. The manufacturer of the truck specifies minimum thickness. A loose fit can mean the hanger points or carriage are worn. Watch for cracks on the arms at mountings and heels.