If a two stroke goes bad, it's because it went lean.....Just to be safe, I wouldn't buy it, unless it was rebuilt and then actually used for a season. That way you know that whatever caused the lean condition was fixed also.
My brother had an Evinrude blow, and a guy I worked with rebuilt it for him. It had to be sleeved even because it had some serious issues in one of the cylinders.
It's been two seasons since then and he hasn't had any problems with it.....A rebuilt engine should be fine....But again I would do more investigating on such a new/expensive motor as the 90 optimax