Isn't it obvious that what was wrong with it is the previous / original owner was a (mentally) lazy moron, incapable of taking the initiative to perform simple systematic problem solving???
Two and four cycle ICEs at their most basic level (i.e. all lawn implements, generators, etc.) need three things to run, fuel, spark, and air.
When I hear someone talking about how they just got their lawn mower back from the small engine shop, I cry tears of Mustachian sadness. Idiots who can't be bothered to change / clean an air + fuel filter + spark plug once a year and clean out an occasional carburetor deserve at least one stout face punch. Unlike a modern passenger vehicle, there are no sensors or ECM requiring specialized diagnostic tools. C'mon people...