Why couldn't Tradehill give the possibility of withdrawing money to moneybookers? Unless TradeHill would demand a chargeback? But then they would be seen as fraudulent?
1) I go to withdraw $1,000 from TradeHill using MoneyBookers. I have a zero balance with MoneyBookers.
2) A transaction I made through MoneyBookers three months ago gets reversed by a scammer. MoneyBookers now claims I have a negative balance and uses my TradeHill transaction to offset it.
3) I complain to TradeHill about not getting my $1,000. What do they say? "Sorry, we did our part. It's not our fault MoneyBookers stole your money. After all, you told us to send it to them."
If you find the excuse in '3' acceptable, then why wouldn't it have been acceptable for TradeHill to just take the thousands Dwolla reversed out of their Dwolla deposits? After all, TradeHill's customers sent that money to Dwolla. It's not TradeHill's fault Dwolla decided to use it to offset scammed transactions.
Any scheme that allows a scammer to steal their customer's money despite no fraud or funny business on the part of their customer is a poor choice for an exchange.