you have mechanics doing free diagnostics? so they use all their tooling and time to earn absolutely no money? Are you visiting actual real automotive mechanics who use instrumentation to diagnose stuff? or are you visiting clowns who stick a code reader and tell you an error for no money?
I ran a workshop too in Pk, nothing was free, diagnostics were charged and if the job was done by us, the diag charge was refunded by absorbing it into the total labour charge. Seems like you want free diag then ultra cheap parts installed by someone who bid lowest. Car repair doesnt work that way.
And yes - you are supposed to study on what brand offers what service and if parts are readily available before you hand your money over.
Btw picanto is a useless deal compared to suzuki offerings if you need to visit forums to ask for scrap parts because the dealer is charging high. And its a known problem as mentioned above that korean and chinese brands have very high service costs which ramp up over the years of ownership due to such issues you are facing.