It didn’t seem that you were asking him to do anything, rather asking *if* he does something.
Also, asking him to read *every* ad in the newspapers and websites he reads is unreasonable. Hakaras hatov has its limitations. If someone gives me a ride I need to express my appreciation, and perhaps to do him a favor in return, but not to give him my house. The OP merely asked if it’s appropriate hakaras hatov to look (“pay attention to”) the ads, but not to read each and every one, as you asked.