Nearly 40 years ago I repaired Mowers for friends,I would tell them what it needed & The only Costs were The Parts.
Things were going Fine until a guy up The Road told another guy where we worked who had just come out from Scotland told me he desperately wanted a Mower so I sold him a mower I just rebuilt for Myself it had a complete overhaul with new Piston & Rings Gaskets & Carby Kit cost to me about $70 I even threw in a New $60 Catcher I showed him how to start it as it would start for me on the First or Second Pull every Time so let him have it for $130.
A couple of days later he turned up & said his young Son pulled The Carby to Bits & now it won't Start.
It took me 10 Minutes to Fix it As The Plastic Needle Was lost.
About a week later he turned up & said it again wouldn't start I'd had enough of him by then as it was virtually a New Mower as everything else was also in Top Condition so I gave him his Money Back then in front of him I primed it & it Started.