When we were looking for our new 5th wheel, and were trading in our old 5th wheel one of the potential dealers said right away that if they needed to replace the tires because they were old, they were going to reduce their offer by $500....they already offered the least of the 3 dealers we were working with.
When we finally closed the deal via email, I found out that from another RVer that if this dealer found anything wrong, they would reduce their previous agreed upon offer.....they had a guy on our rig's roof before we got out of our truck.....they wanted to see that the major systems worked......they were impressed at how good our 10 year old was...including new tires - but, they didn't give us any more.
If you trade it in broke, don't be surprised if they lower their offer.
Good Luck.