Are the joist hangars to supposed to be the same size as the joists?
Is there a 2% slope rule for this? Any other issues. The buyer said he heard from another inspector that this was wrong on another home he had bought in the past. I told him I would look into it. Thanks.
Joist hangers should be the same size as the joists.
Those are undersized.
2% slope for what?
It’s pattio cover. What difference would it make?
No live loads.
I suspect it is fine. See the attached Tamlyn chart, i.e. a 2x8 and a 2x10 can use a 7" hanger. Did you measure the joists and the hangers?
I’d be more concerned with the albino support column that was added to stop the deflection of the main carrying beam.
Could you ask them to jack it up another inch or two? :)
The carrying stick needs more than jacking, take another look.
The joists were 2x12’s with hangars that were 2x6. The 2% rule was for drainage.
can’t tell what the partial covering is but most decent drainage basic rule of thumb is calculated at 1/4" per foot or grater even for flat roofing materials
1/4" per foot is 2%. 
It’s a sun screen not a roof. It isn’t meant to shed water so don’t know if the 2% slope is as important.
What else are you suggesting?