i useto work at a quick lube shop, and all the extra or premium services are pushed for a few reasons, 1 is the owner claims that oil alone doesnt cover the bills for the day(right, i didnt buy into that) the other is they are commission bonus's. i sold a insane amount of engine flushes ...almost every car, and when you are doing 4 cars at a time, at $1 each extra and each car takes 15-20 min, on a busy day the $ adds up. then the tranny service(t-tech) is $5 or something , and same with the injector cleaning. (also the extra certifications give you quick raises there...somehow i was safety and fire extinguisher inspector..extra buck a hour..hell ya)
now i can understand the engine flushes are bad, in fact i refuse to use them on my own cars now that i know more about them. the thing that scares me is the managers when we ran out of engine flush filled the bottles with tranny fluid...now that is wrong. (owners had the store pulled from him that i worked at, i warned him of a few things and staff but he didnt listen and the "manager" i told him to watch out for robbed him blind, he lipped off to me once i left and told the owner its me or him, and with him there hes going to loose his business, he said hes a cert mechanic and hes a good manager..boy was he wrong about both,fake resume...1 point for me)
injector and fuel system cleaning i cant see doing any harm, except to the spark plugs maybe, we useto use some sort of snake scrub and clean the intake by scrubbing it, turned out very good.
transmission service i wouldnt let them touch (manager tried to "seal" a customers tranny pan with spray paint...nuff said....) and the coolant flush i dont see a problem with.
the coolant and the tranny flushes actually change the fluids based solely on the cars pressure and fluid circulation, so the machines themselves cant do any harm, just the techs.
bottom line, dont use quick lubes for anything but oil, and dont do a engine flush.