What don't you get?
One was a mate, one was a customer. Customers come and go and often have no loyalty to a supplier but your mates are your mates...
That said, a business lives and dies by the quality and reliability of its services so deliberately sabotaging a customer - unless you can be sure there is absolutely no way it can ever, EVER be traced back to you - is not much better than walking along the bottom of the Great Barrier Reef wearing concrete overshoes, dragging 50 kilos of sharkbait and carrying a sign saying 'bite me'...