Bring an indicator and a couple of 1-2-3 blocks and use them to check tram of the spindle to the table and the amount of backlash on each axis. Run the spindle through all speed ranges and make sure it doesn't make any alarming noises. It wouldn't hurt to check runout inside the spindle nose as well. Problems in any of those may not be deal killers but could be good negotiating points.

Will you have any problems getting it moved out of it's present location and into the new one?

Unless the seller is to renege on the deal, it can be a good idea to bring cash for a down payment to seal the deal and take some of the tooling when you leave to dissuade someone else from offering to pay more than you agreed to. Best is to bring cash and means to transport the whole thing back home at the time of inspection. If you tell him you'll be there at a specific time, either be there at that time or call to let him know you are delayed. Motivated sellers often just want it gone and you don't want to lose out because the seller thinks you may be a no-show.

Mike