13K sounds like a good deal for a 1998 X-star. Some things to know offhand would be that this was direct drive not a v-drive in 98. Also, I don't think they came with towers from the factory but maybe there is an aftermarket one on there.
The hourmeter will turn if you want the radio on and leave the key in the "on" position. The radio will come on and the hourmeter will not turn if you have the key in the acc (accessory) position (counter clockwise). The owner is partially correct here.
Look at the overall condition of the boat, is the interior in good shape, is there mangled sets of stero wires hanging out all over the place. If anything appearance-wise is not what you'd expect compare it to the selling price and determine if you can live with it or fix it then forever hold your peace.
The next think I would look at is condition of the motor. I would think at a minimum you should take it for a test drive, but don't do this until you have the cash ready to go or you're wasting your time and the seller's time. (Unless he is going out to the lake anyhow then maybe you can bro down and get a few pulls to boot). You should probably pony up some gas $$ for the test drive (unless it doesn't run
If you really want to be thorough, take it to a shop and have a compression test done on the engine. This is fairly easy, the mechanic will pull the plugs and be able to see how worn the engine is by how much pressure the cylinders hold and for how long.
If you need to trailer a lot, take into consideration the condition of the trailer. They are generally pretty cheap (2-3-4K) and replacements parts are readily available to fix ones that aren't too beat.
If you decide to buy it, dump the oil and trans fluid right off the bat, probably do new spark plugs and a new impellar. The idea here is that you don't know when the last time the previous owner did this (unless maybe he has maintenance records).
You can use hours as somewhat of an indicator of the condition of the boat, but I wouldn't pass it up soley because the hours seemed a little high. (As a comparison my 99 X-star has 780 hours on it and still runs great).
My only other suggestion is once you've had a good look at it. Get your $$ ready to go the next time you talk to the guy, don't waste his time, have the cash ready to go as soon as you are comfortable with the decision then you can dicker with the price if you feel you need to. The owner will be more receptive to price adjustments if you can get him paid within 24 hours. Maybe do a deposit (check only) and a bill of sale to lock them in if you think there are a lot of other interested buyers.
Lay down a fat stack of ca$h (ok not really a cashier's check would be much much better) and go enjoy your new boat.