If the unit did not have any roaches when it was given to him, and your lease states that it is their responsibility, they should pay for it. Since you already got the problem taken care of, I can see how it might upset the tenant that he'll have to pay for it. I'm sure if you told him before hand that they have to pay for pest control, that might have changed his mind about whether he wanted you to take care of it or if he could have just taken care of the problem himself. Regardless, the lease says what it says. If you go changing it at your discretion, they could find many more issues for you to fix. For next time, I would let them know when they call you, that it is their responsibility, you could get someone out there to fix it, but you will have to bill them afterwards. Then they have the chance to say no and fix it themselves if they don't want to pay for a professional. Although from a landlord point of view, I'd rather have a professional do it, rather than the tenant.