Sounds rather impossible to me, or i must be missing something.
How can you have 1 deposit address, but credit individuals who each deposit coins to this address?
The only ways i can think of are: making the individuals sign a message with the address they used to deposit the coins (so everybody using a webwallet will have problems) OR forcing the individuals to divulge the address which they'll use to deposit coins beforehand (and only credit coins to an account when one of the input addresses is an address that was pre-divulged).
It's 2016, and nothing is impossible.
But, yes, it is impossible for a marketplace to only has one deposit address unless everyone is using the same account or, at least, have something like "Which Bitcoin address you will use to deposit your funds". But, I think what he meant was each account will have single deposit address.
