southwest rv ripped me off on labor and parts glendale, Arizona

I took my generator to the rv place to service the unit for not getting a spark to the plug,  that it was working fine, but running a little cold and having trouble starting it.  They told me that it took 4 hours to fix, with the unit being out of the rv.  they also replaced parts that I replace two days before I took it to them, trying to make money off me.  Then before I went to pick it up I called around other rv repair shops and they told me since I had the unit out of the RV that the worst it would be was 2 hours for them to fix it.

I feel that I got ripped off with them charging me double the labor and with them charging me for parts that I already replace 2 days before. 

I guess thats what I get for taking it to a mom and pap shop.