My boss's son is looking to buy a different house and just asked me if I
tried the LendingTree route to find a lender with the best rates.

I didn't, because I got tired of the used-car-salesman tactics I encountered.

I told him I would see if anyone here has found a good online lender,
or good experiences with services like LendingTree.

Good experience here with Lending Tree.  It's true, they will duke it out - matching or beating other offers, eliminating fees and such.  The offers you get will give you the specifics and 'fine print' ie. closing costs, points, etc.

Once you make contact with a bank/lender over the phone, all I had to do was tell one lender what another was offering me - and he knocked off a couple precentage points, without verification.

I'd use them again if I had too.