I own a used SM150 - the SM150 has five 18x18 inch shelves - the SM250 has six 24x24 inch shelves, man that's some party you'll be ramrodding !! I got my 150 for $1400.00 and felt like the lady in the Ikea commercial running out of the store yelling at her husband "START THE CAR"...
http://www.youtube.com/watch?v=6C7oqXewyCEThe SM250 has the IQ4 controller, 6 huge shelves and is exactly like the SM260 (click on the COOKSHACK BARBECUE & SMOKE-COOKING CENTER link below my post and look at the Commercial models to find the SM260 which is your model but in Stainless on the outside. Also, since this is likely a former restauranteur selling it, ask if he has hotel pans, tongs, any smoking wood left over he also wants to sell. When I got my SM150 I got a whole boatload of extra stainless steel hotel pans, 1/3 and 1/2 hotel pan inserts and lots of hickory for an additional $60.00. A real score in itself.
Sheesh that is SUCH a deal... Run don't walk. I would suggest a simple investment for the unit, order the cover from Cookshack to protect your SM250 (see, I'm already calling it "your SM250").
I started out with an older SM008 which got me hooked on smoking meat. The SM250 is such a terrific unit, you go so much capacity you could open a restaurant with it. Matter of fact it is already NSF (national sanitation foundation) "approved" and with a decent cleaning would pass a health department inspection easily.
Let us know what you do. That is quite a good deal.