I bought a TT in the last 60 days and paid for it myself. You might try negotiating that you'll pay for it, but if you buy the trailer, they reimburse you for the inspection. Normally I would have done it myself, but the TT was 2600 miles away.
On edit, a couple of other points. If the seller told me he already had an inspection, I might be a little suspicious of it. If the inspector misses something and you find it after the sale goes through (let's say the water heater has a crack in it from bad winterizing) then you're going to want to go back against the seller because he represented it as being in good condition. He's selling the RV "as is, where is", not with based on an inspection he paid for. He's not going to want the liability. If I'm paying for it, the inspector is working for me.
Bill