Your is a possessive form of the pronoun YOU therefore, it shows that the word following it is a possession to the person in speech. in this case they used YOUR customer to show the customer is the possession and if he/she is neglected YOU are the one losing money.

Hi Bogdan, it's possible that in this situation, it's not literal. The way I interpret your sentence is the following: if I neglect my customer once a purchase is completed, he or she will not be my customer in the future, therefore I lose money in the future. For this reason, since it's not yet my money (but rather, money in the future), I cannot use the possessive form "your," so I believe this is why "you" is used instead.

This is an interesting contstruction--I can see why it causes confusion. "Losing you money" is a way of saying it is causing you to lose money. So YOU is not an adjective that should be replaced by YOUR. Some other examples of this type of phrase are: This is causing you pain. This is bringing you joy. This is gaining you respect (although that one's a little odd).

In other words, “you” is an indirect object in this sentence, where the direct object is “money”.