This may not necessarily be a longarm. The 2ft wide and 2 ft high, is a bit confusing. they may be referring to the depth of the rack is 2 ft. At only 2 ft high, does this rack sit on a table top or is that the height of the machine? I am pretty sure Nolting's smallest size is the fun quilter at 18" throat size, but it could be an older machine so don't know if they made a smaller machine prior to that or if this machine has a larger throat. I am thinking if the 2ft wide measurement refers to the machine head itself (as opposed to the rack) the machine is most likely 18" throat. I am also guessing at that price (600 British pounds = around $950 US dollars) it is not a stitch regulated machine and more than likely an older one. Nothing wrong with unstitch regulated. Tons of people have them and learned on them.
First question would be is the machine in good working order. Second is "can I come and test the machine?". After that would be based on your wants and needs. I would ask the last time the machine has been serviced, is there local support available if it should need servicing or you need help. Are the rails and carriage in good condition and does the machine move smoothly (although this can be tested by you if you decide to go see it). How deep is the machine throat. How much does the machine head weigh? (so you know how much help you will need to move it and / or get it to a servicing if that becomes necessary.
Questions to ask yourself do you have room for a large rack setup. Don't forget you will need room to work from the front and the back of the machine so you will need room to walk around it. Also if this is a table top rack you will need to buy some sort support for it.