It depends on how much your LOCAL retailers sell Swarovskis for and how much your customer is willing to pay.
Some customers want BLING BLING BLING nails without paying much for them, so there is nothing wrong with looking for alternatives.
My salon offers both authentic Swarovski and a Chinese-made alternative, and we charge 1$ per stone for Swarovski, 15 or 20 cents per stone for the Chinese made ones. We often recommend our customers getting the Chinese alternative for all stones ss12 and under and getting Swarovski for ss 16 and 20 because with these larger sizes they start to show visible differences between the real and fake.
For example, a single long nail fully covered by stones takes about 60 pieces of ss6 and ss8 + a few ss10 and ss12, we usually end up charging 10~11$, which pays us enough for the 10 minutes it takes us to do.
Is there a HUGE difference in terms of sheen? No, you just have to buy the alternatives from the right vendor, so they are comparable in quality to the Swarovskis. My boss spent her time and money ordering from different vendors and figured that only one place on Aliexpress has the best to offer. My boss always pays for DHL shipping so the stones come fast. Their free shipping supposedly takes forever.
FYI, here in the US, a 1440pack of Crystal AB ss7 is 46~48$, Crystal ss7 is 33$.