Let me get this straight, to make sure I've interpreted this right
[customer contacts shopto twitter with DM about whether they will drop price]
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[customer chats with friend seperate to previous interaction, voices his displeasure, does not tag them or anything though]
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[shopto takes to reading customers feed, reads the independent conversation, takes initiative to contact customer, asks for account number, could be related to the 1st interaction, customer provides and instead rep uses it to put cusomer on the spot and delete their account]
That's how I'm reading OP. If that's right, pffft, that's terrible. Regardless of whether he badmouthed them or not, that's pretty bang out. You can't try and strong arm genuine word of mouth like that. Or you can, and people stop shopping with you.