Small business owners. WWYD?

What would you do or what can be done (if possible) if you caught your employee secretly stealing potential customers from you during work hours. I’m currently employing someone who does good work for me but I have caught them several times while they were on the clock “giving quotes” to customers who are inquiring about our services. They see the work we do because it’s clean and we try to give our customers a good experience. Several times the neighbors or passer by’s would inquire about our services.. this person that works for me has frequently given discreet quotes to our customers and to new customers behind our back. Sometimes pocketing money for extra work they offer while using our equipment. They have also been on the clock and left job sites that we did not know about or authorized for them to do to give quotes to customers inquiring about our work. We suspect that they have been offering the same services on their days off but are keeping those customers for themselves.

I don’t want to be a crappy person or are trying to be greedy but I feel like we have bent our back for this particular person. Offering higher pays, giving other incentives and doing a lot of additional help including monetary help just to help them keep afloat. I think we go above and beyond the extra mile for our employees and they consistently thank us for everything we do (not to brag about this). But it feels like a slap in the face. Is it just me? Or is think something we should just let go of?