Business set up

I do not know if the title is appropriate or not . But via general conversations and on the hpacademy podcasts as well as my personal experience its really hard setting up a healthy business . I have just recently done the jump to open my own shop yet I feel like I am running a child care centre or something of that sort . Customers coming in and even after spending hours of explaining agreeing etc. Yet do not understand .

An example I had a customer bring me his car for diagnosis due to oil pressure. I told him we have to pull the engine apart no worries we do it . I was right oil pick up broken , crank pulley broken , metal shaving , crank damaged the whole lot . We discussed his options . He decides to go to forged. He askes me if its OK to bring his parts as my parts one of suppliers is his mate and the one that introduced us . I agreed . 4 months later he brings the parts and tells me you know what you should hurry up cause you have the car for so long here . I explained to him it was impossible for me to assemble the engine without rods . Anyway a whole drama of a person .

I have another customer for whole rebuild which brought me the engine after I gave him the time frames and explaining if we need to go just through a general recondition x amount of time then if we need to do oversize pistons etc x amount of time . All agreed upon. Yet he calls me up after I have taken the engine out , and tells me keep in mind that in 2 weeks I am going on vacation with the car . Yet that wasn't either discussed nor was i informed nor is it in either time frame .

I have heaps of example for only a short time of period of operation. I work on almost exclusively atm on a specific brand and it's a nice market .

My question to anyone is how do you deal with these people? They do not say the truth when they are on the forums or car meets , they will easily talk bad about you and your shop regardless and i can't find a way to work things around this issue . How many customers can you fire ? How many times can you make each of them come over to sign a paper stating your communication and what was discussed. Like you are a grown human being you have the right to vote and Yet I have to sit you down all the time and spend x hours unpaid? Or do I have to tell you come over sign this paper and I am not doing anything till you come ?

TIA