I'm not going through 9 pages so I'm sure this has been repeated.
NEVER let a person rush you through anything you sign off/for.
Tell them to go pick their nose go stand in the corner, whatever !
Once you sign the dotted line you own it !!!
Had you noticed it when they delivered it, it would have been a different game. Now its yours and you get to deal with warranty and getting it fixed...
Just like taking your car/truck/rv in for service work, walk it with the sw and walk it with them when you come back to pick it up. If it was under the hood work pop the hood and look around etc.
I worked in automotive service end for years and have seen both techs and customers try to get away with just about everything!
Good luck and hope it gets taken care of !