Two stroke engines were VERY common on lawnmowers before the mid 90s. For example, all Lawnboy lawnmowers had two stroke engines before 1990. Most of the major lawnmower manufacturers offered two stroke engine options back in the day. The Wisconsin Robyn two stroke was a popular option on Snapper's commercial mowers (Snapper homeowner mowers had a Tecumseh two stroke option). Toro also offered the Suzuki two stroke on their higher end homeowner models. The only thing that would kill it was long-term dirt ingestion.
Having been in the business, and having sold and serviced MANY Toro Commercial mowers, I can say without hesitation that this was the best, most reliable, and most durable 21" commercial lawnmower ever produced. Everything about this mower is bull stout and it is extremely heavy. If a homeowner bought one of these it would be the last lawnmower they would ever buy. At the very end of production they sold for $1300, definitely not chump change, but worth every penny. Having said that, the seller is being quite cheeky with the price considering that they have been out of production for nearly 25 years. If it runs as good as it looks it would be worth about $600 IMO, still not chump change, especially for a 25 year old 21" lawnmower. The commercial guys that I know who are familiar with this mower would jump all over it at $600 (some of them are still using a few of these, that is how good they were).