Should I buy a used professional-grade chainsaw?

Yes, if you know what you’re looking at. A used pro saw is almost always a better value than a new homeowner model — pro saws are built to be rebuilt, while homeowner saws are disposable. Inspect it for compression, piston scoring, and wear; if it looks clean and starts cold, you’re good. But skip it if you can’t tune a carburetor or replace a fuel line.