You slip the doorman $50 to hold tracking numbers of packages you're having sent to random units in the building. Or just promise him a unit at MSRP for his help.

These sorts of things are pretty cheaply routed around for those making scalping into a volume business.

Sure you can probably lock things down so you catch the vast majority of these mechanisms, but not without impacting legitimate users. So it's a tradeoff of how much more of a hassle do you want to make things for legitimate customers vs. how much you want to lock out resellers.

You don't even really need a doorman in many buildings either. There will be a shared mail room (if you're lucky) where packages get dropped. If you work from home you just watch the UPS/Fedex tracking and run down the moment it gets delivered to snag it before anyone else sees it.

The few folks I know who did this sort of thing were less professionals making a living off it, and more someone who wanted to subsidize their gaming habit by grabbing 3 or 4 units and keeping one while flipping the rest. They'd just ship to friends/family. The folks buying 50 units at a time are pretty rare from what I can tell.

I have since moved out of NYC but yes I had an apartment number. If the doorman was helping this scalper, the scalper could have varied the address he used enough to avoid exact match dedupes while still ensuring he could claim the packages as his from the doorman.

Doorman buildings are quite common in NYC.

[edit: to be clear they are not the norm, they are more expensive than buildings without one, but there are still lots of them that are not Trump Tower or other places for the absurdly wealthy]