OK, as an owner of a W124 for the past 5+ years, let me clear some misconceptions. First, if you drive in a hot day with the AC ON in stop and go traffic the coolant temperature needle will creep up. Think about it, there is no way the coolant temp is going to be the same when traveling at highway speeds than it is when driving in stop and go traffic. The coolant temperature needle on the W124 is very accurate and linearly calibrated so it shows temp changes in a dramatic fashion. What you DO want to make sure is that when the AC is turned ON, both aux fans turn ON at low speed. When the coolant temperature reaches 110-115C, the aux fans switch to full speed. While this is the way MB designed the system to operate, several people, self company included, feel uncomfortable with the temp reaching 115C and there are mods available to address this. By far, the best solution (I've tried several) is to replace the stock viscous fan clutch with a "tropical" model that engages at lower temps.
Secondly, if you think that because a 14 year old car with 170+K miles has a tear on the leather seat it means that the owner has neglected the vehicle, think again. I keep my W124 in top mechanical shape. I've spent well over 10K in repairs in 5 years and most of these I've done myself. My vehicle has had the head gasket, engine wiring harness, and many other critical items replaced. I use Zimmerman X-Drilled rotors (always had issues with warping stock rotors and '95 W124s are known to do this). Having said this, my driver's seat has a tear in the leather and the lower front bumper has a few minor cracks (impossible to avoid driving in the Philadelphia area) and I decided that I will not spend an exhorbitant amount of money to repair cosmetic issues in a 14 year old vehicle with 222+K miles. I spend money where I deem it more necessary (mechanical condition of the vehicle). I would not consider myself an owner who neglects his cars. I've always maintened them properly and kept them in great overall shape. This time around I decided I will not spend several thousand $ in cosmetical issues on a car that is not worth that much anymore. This is my opinion so I would say that don't stop from buying a 14 year old vehicle because it has a tear in the leather seats. DO make sure you obtain records and DO make sure the head gasket and engine wiring harness has been replaced.
Good luck!