Should the police take the money without cause? No. Can we question what he was up to? Yes. It's risky, as cash can be stolen from you with no recourse. It's also a very inconvenient way to pay someone, since it's physically large and would take a long time to count out.

I think you are vastly over estimating the size of 80K USD in $100 bills. Each bundle of $10K is about 1/2” thick. You can easily carry 80K in 100’s without looking out of place.