Hi Big_Blue,
Welcome to ALR. I would take a bore light, a cleaning rod, a .45 jag, patches and gun oil with me. The first thing I would do is check to see if the gun is loaded. To do this put the cleaning rod down the barrel with no patch. Mark the rod at the muzzle, then withdraw the rod and lay it along side the barrel, with the mark at the muzzle. If the gun is not loaded, the breech end of the rod should be within about a half inch of the breech end of the barrel. If it's an inch or more, suspect it is loaded. Another test would be to hold the gun vertically, muzzle up and drop a metal tipped ramrod down the bore. If you hear a metallic clank, that's a good sign. A dull thud, suspect it is loaded.
Once you've determined the gun isn't loaded, drop the light in the bore and if the bore is dirty, remove the light, then give it a wipe or two with an oiled patch. If the patch comes out rusty, or worse, it's all snagged looking, the bore is likely pitted, probably because the rifle was not cleaned properly after every use. If so, pass on the deal. If the rifle really is new, don't be surprised if the patch comes out with black cutting oil and metal shavings from the machining/rifling process. That's a good sign, it's likely never been fired.
Once you are SURE it's NOT loaded, I would cycle the lock, if it's a flintlock, open the frizzen, then pull the hammer back and listen and feel for the sear to drop into the half-cock notch. You should hear a crisp clunk sound. Hopefully the lock has a half-cock notch. While it is at half-cock, bump the stock with your free hand or bump the butt-stock on the floor, to see if the notch holds properly. Pull the hammer on back to full cock, again bump the stock to see if it holds. To uncock the rifle, hold the hammer back with your thumb, pull the trigger and ease the hammer down to rest. Take note of how the trigger pull feels. If it has set triggers, check their function, if it's a cap-lock, don't let the hammer fall freely on to the nipple. If it's a flint-lock (and you are SURE it's NOT loaded) and it has a flint in place, close the frizzen and dry-fire the lock. Does it throw sparks?
Regarding the price, for $250 of my money, the rifle would have to be new or as new, nice wood, shiny bore, crisp lock and triggers and even then, I would start my offer in the $150-175 range, as see what happens.
I know I'm forgetting something, so others please chime in.
So, Big_Blue, are you a Wildcat fan?
-Ron