A forklift should be checked correctly and given a test run prior to purchasing it. This applies specifically to trucks being obtained on the World Wide Web. It is really important to detect possible problems with trucks acquired from businesses online.
Be sure to start the engine from cold, and note the ease with which the engine turns over and whether there is excessive smoke. This is especially crucial with trucks that have IC engines.
The test run should include a check of the truck's performance in tough situations. A skilled driver could maneuver the truck in reverse and forward, up the ramp.
You could check an IC engine truck yourself. On a clear part of floor, run the truck around for several minutes while a qualified driver tests the hydraulic functions. Afterward, look at the ground underneath for signs of fluid leakage. Even seemingly minor leaking could indicate serious problems which will be really costly to fix later on.
A qualified person should check the masts and chains. Check with and without a load that the mast operates well. Watch for sticking or 'binding' of the mast. A warning indication is play in the mast channels or between the fork carriage and mast. One more is creeping forward or creeping down of the mast when loaded. These could be signs of issues with seals, ram or valve.
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 checking the forks, look closely at the heel thickness for damage or wear. The manufacturer of the truck specifies minimum thickness. A loose fit could mean the carriage or hanger points are worn. Look for cracks on the arms at heels and mountings.