Looks better than Forum. The Debt is better for you then discarding another card.
Sure, with more copies it becomes more tricky to evaluate but a card that is better than a $5 while only costing $3 if you only run one copy of it is most likely totally out of balance.
There are times that Businessman could be better, times when it's the same, and times when it is worse. Forum is fairly weak in its end result - it's a sifter that ends up resulting as a cantrip. In an optimized deck ("junk" all trashed), Forum is a waste of a $5 purchase. It will always leave you with the same number of cards (default case, I'll say leave you with 5 cards in hand). In its best case, with multiple Forums, you end up getting the 5 best cards from your deck into your hand.
For Businessman, it's first play will leave you with 6 cards (default case), but also 1 debt. As an opening purchase, that means you could end up with $6 (if you open Businessman/Silver) if you draw cards right. This is relatively strong, I agree. However, if you try to play a second (either double Businessman opening, or later in the game), then you end up still with 6 cards and 2 debt after some sifting. A third played in one turn just doesn't make sense - ending up with 5 cards and 3 debt. So it's very limiting by mid-game.
I've updated the cost to $4, to show that it's mostly better than Warehouse and overall worse than Forum (even though a single play may be better some of the time). And I think that's okay, since dealing with negative tokens will sometimes have varying power levels, I suspect.