Amazon is like 44% of e-commerce sales in the US. I don't even need to check to know that's likely the highest market share any single retailer has.
Still, it's impossible for us to divine some real numbers outta this, but if it's consistently doing well on Amazon's best sellers list that's great news. I mean, the PS4 version is hanging next to the fastest selling exclusive on that console in the US best seller's chart for PS4 games. That list gets updated hourly. Its got legs for sure.