I want to get a 3% discount on buying 500 BTC.
Owning Bitcoin is already an investment, why would you want to have a % on purchase. I will advise you to avoid such offer less you regret it by falling into the hands of scammers. It's your money, but if you want to get such discounts, then go invest in new Alts projects that you have made personal search, know their office a d sign an agreement with. Because 500 BTC is huge money
He want to get an instant profit by buying bitcoins at his desirable condition but actually I don't think there are people will click this offer since in the first place we have so many exchangers around and anyone can sell there bitcoins at reasonable price instantly and safely. But I will not recommend him to invest with alts since it's another story and huge chances for him to lose those money he have and much advisable for him to remain at the current rate or buy at the cheapest on exchanger which accept fiat deposits and earn later when market pumps.