I think the idea was that they’re suggesting to difficult customers that the shop did not want them to return. They could afford to do to such customers because of the whole 20/80% business statistic thing.
All well and good that a business can afford to ditch customers but "difficult customers" is a often a term that reflects more on staff which have poor interpersonal skills. Such staff/owners can't fathom why some people want to know what is wrong and how it will be fixed, usually because they've been stung by unscrupulous mechanics before.
Such customers have a learnt mistrust of the trade though experiance and the industry does such stuff cause they want to be better regarded? It's funny, but it's fcuked up.