I know that the ignition is very expensive to repair on the 9.9-15 should it fail. Unless it is a very very good deal I would keep on looking. Make sure the engine is at least started up for you after a good inspection.
I paid $400 for the motor. it is in great shape cranks and runs good, and it came with a 5 gallon tank. Probally could have found a better deal if i could have waited. You know how the prices go up a little in the spring and summer months.