I'd bring the following if checking out any used ML: ramrod w/several size jags/patches, some lube/oil for patches, vernier calipers, screwdiver(s), nipple wrench and bore light.
Swab the barrel with wet patch and feel for tight/loose/rough spots. Run a dry patch down the have a look with the bore light. Take the calipers and run them down the lenght of the barrel to check for bulges. Is the barrel crown in good condition? Before patchwork/bore light see how far the ramrod enters the barrel with the jag and compare this to the length of barrel minus the breechplug (e.g. is there a load in there?). I don't like looking down a loaded barrel............
Look for places that work has been done on barrel such as adding sights/mounts (e.g. holes/screws/dovetails added).
Check the funtion of the lock/trigger assy. Good strong spring, hold at half cock, hammer line up with nipple. Bring a rubber cap to put on the nipple so you can test dry fire. Does the nipple unscrew easily.
Check stock for cracks. Particularly the wrist and about the tang/lock inletting. Most hawken types this can be done by removing the barrel and taking out the screw that holds the lock in place. Is the hooked breech a good fit and is the wedge pin(s) tight.
How is the hardware, are the screws in good shape or has "primitive Pete" (no offense to any members named Pete) been using butter knives to screw/unscrew things.