Start by turning on the refer so it can cool while you do the rest of the things. Put water into tank {fresh tank} turn on pump and run water to all faucets and if outside shower don;t forget it. then have them run a hose so you are on city pressuer. then look for leaks. Every one of my rv's have had a water problem that is not discovered during pdi. No one hooks up water. My present one the outdoor shower was broken. It froze because someone didn't flush out the clear water when adding pink. Run 120 volts to unit and make sure all appliances, etc. work.
Don't let them tell you it's too much work or we haven't the time. It's your money and it will be hard to get them to fix it once you leave. Hold the check or at least a goodly portion of it until you are satisfied. My fifth wheel had issues and the owner of the business wanted to charge me to repair them. It was brand new. I told him go to hell, that I wanted my check back and that I would come back in4 days to pick it up or the deal was off. Money talks because it was fixed and we had an excellant camper for 16 years.