otc offers you encounter are 99.99% fake in my experience. 
Ditto that.
Also you are trying to buy Bitcoin in the middle of a bull run and asking for discount. And not just for 1 or 5 pieces but 500.
Bruh...
Nobody in the right mind would make you a discount. They'll ask a premium from you instead.
If you are lucky they won't ask more than %3.
