Degrade, minimize, or diminish. Those words mean cheapen.

Cheap is an adjective cheapen is a verb.

Don't cheapen your self by compromising your standards.

The verb for cheaper is cheapen.
Other verbs are cheapens, cheapening and cheapened.

"We will cheapen this later".
"They are cheapening their older products".
"The bananas have been cheapened".

Sully means to dirty or damage something, or cheapen it- usually symbolically. "You will not sully my good name with false accusations."

Tourism can cause the people of a nation to have pride in their history and attractions. On the other hand, it can cheapen the experience of living in a great city.