That means nothing. Did you get in in writing the belt is good? There is documentation it has been changed? It has needed to be changed at least once.,
What is the recommended maintenance interval for the belt, and is it in time or miles? Other vehicles I've owned called for timing belt replacement every 60-80K miles, which would normally be somewhere around 4-8 years, so yes, it should have been replaced at least once. It probably has been, but if it's not documented, the next owner has to just bite the bullet and get it done to be safe.
As Azblue says, there is no way the timing belt and water pump can really be inspected without doing the work to do the actual replacement. All the inspection shop can tell you is it's fine right now because the engine is running and coolant isn't leaking out the front. But, 15 minutes after the inspection, all bets are off. For that reason, timing belts have to be changed on recommended time or mileage intervals. Water pumps that are driven by buried timing belts are usually replaced, whether they need it or not, just to insure you won't have to go back again prematurely.
I
THINK Toyota designs "non-interference" engines, but YOU will need to confirm that, along with trying to research the maintenance history of the truck to confirm the date/mileage of the last timing belt change. A "non-interference" engine is designed so that if the timing belt fails, then the moving pistons don't hit the valves that have quit moving. If yours is a "non-interference" engine, then you are simply stuck on the side of the road waiting on a tow, but at least you won't need a new engine. If it's the other kind, then a timing belt failure leads to unmitigated mechanical disaster.
