Your last remark is the best option. That is…. IF the guy will refund his $$$$.
As for the problem, I’ll throw my .02 in too.
There is a very good chance the CDI is junk if someone turned the engine over vigorously with no plug in the boot to ground it. I’ve seen this happen, stupid brother! Attempting to pump fuel to the carb he hit it with the starter, with no plug. When I told him he F***ed up he inserted a plug and BBBzzzzzzuuTTT!!!!
That box was LOADED with juice, and it never sparked again.