Advice against car dealer

r/

Location: Maryland
I bought a truck from a dealership in pa. (Last week)Truck was spotless, dealer I thought was being very upfront with all of the issues I would want to know about.
I took the drop in bed liner they installed out today, and the bed is completely rusted through and there is a hole at the front. They obviously did this to hide it. I reached out to the salesman today, he said he forwarded it to his manager. If they come back and say they are not fixing it, do I have a leg to stand on legally?