you are living in Pakistan. realize that.
You will get ripped off in any job if you dont know how to measure results. Your airconditioner at home was probably never vacuumed when being installed so you have adulterated gas charge, This causes no pain to the installer but the owner pays with his/her wallet. While naive people like you just proved yourself, would say
"chalraha hai - thandi hawa maar raha hai, AC set hai"
same case on cars, if you are asking for a complete overhaul of your car and then ask for a shop - you are not ready to dive into this. - For testing, go ask some shops on the exact jobs you want. Price them out and pay according to what you like.
I personally have overhauled a lot of cars, Own hands and labour, Getting this job in Pakistan by being wallet holder is a 95% chance of getting ripped off and car getting scrapped.