Took my mower to local repair shop and he said it needs a new head. Apparently the valve seat came off and bent the valve. He said he replaced the valve seat and put in a new valve but after letting it run it happened again and bent the new valve too. Just curious if this is common or if someone else has had this issue? Just haven’t heard of someone replacing a head on a mower before.

I've read that after doin such a repair, it helps to "stake" the steel seat in the aluminum head.  IE, many small dimples very close to the seat pushing the aluminum making the fit tighter.  
 
I have the same issue on a Briggs 18HP Zero turn I picked up about 3 years ago(built in 2005). 
Replaced the head and piston, runs great.