Years ago I gave a few rolls of B&W to my local photo shop to develop, they had to send it out but when it returned it was completely blank (not orange). It had been put through the C41 process but what was weird was that the sales guy at the shop tried to blame me by saying this was a unexposed roll of film I'd handed in. I argued that it couldn't be as there was no edge markings, hence the lab was to blame. He told me that cameras put the edge markings on the film, hence no markings, no exposures! Took a lot of explaining for him to relent and a lot of time for the lab to properly compensate me (they tried to fob me off with one free roll of generic colour film).