i just finish an overspray SUV , bmw black...so here is my input on this.
- use red meg claybar , not the prep towel , the towel is psy when comes to this kind of jobs
- use a good lube , i prefer last touch meg
- be ready to do 1 step polish for any darker color car , or quote all the cars - that way your remove any marr left by claybar
- be ready to do 2 step correction on black cars
- be specific about what you quote, what`s included, an estimate realistic time
- add extra time , on this jobs are always surprises
- have some terminator handy, also some gogone may be handy for rubber trims etc...
- have a few helpers
- have some blades for windows
- quote only exterior that way you may be more affordable
- make sure upfront about the availability of each car
as a rule of thumb do a test spot and after that give them a quote, that way they see what results you got , you know what you deal with and everybody is happy

- overspray cars are a pain , it can take you more than a correction

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i charge 600 for an suv blk , 2 step correction exterior only , and removal of overspray/ home latex paint , a bit cheap but was ok , done with 2 helpers in 4 hours.