Debt condition abuse?
If you have ANY condition (whether it be debt, or a dark pact, or hallucinations), you cannot gain it again while it is in play.  So, if you take a debt (getting 2 additional "bucks" or influence for that purchase), on any subsequent turn while you are still in debt you cannot do that again or get the bonus.  It only happens once.

If, on a later turn, you are able to rid yourself of your debt (e.g., through its reckoning event), you can take on another debt to get the 2 additional bucks for another purchase.  But this is only available if you can clear the previous debt condition, since you only get the 2 bucks when you gain the condition card.

EDIT: The official ruling is found in the Reference Guide on p. 4 under the "Conditions" header: "An investigator cannot have multiple copies of the same Condition. If he would gain a Condition that he already has a copy of, he does not gain another copy of that Condition." and "If a Condition’s effect does not list a limit, it may only be used once per instance of the triggered event."

It is probably discussed in the manual too, but I find it is easier to look things up in the Reference Guide, generally speaking.

The above should be understood in conjunction with the Bank Loan text on the board: "When performing an Acquire Assets action, you may gain a Debt Condition to immediately add 2 successes to your test result".  Again, you can only gain a condition you don't have so this only triggers once, when you gain the debt.