I am out of coins. I need 2 Euros to acquire my next route. Loans are 5 Euros. Do I get 3 Euros in change? My competitor say the rules do not specify change, so I don't. I say change is logical, so I do.
You do not get "change". Loan cards are simply a penalty for playing a route that you can't afford to play. The loan is not a loan for 5 Euros, rather it is simply a card that counts as minus 5 points at the end of the game. The rules don't distinguish between being only 1 toll token short of playing a route or being short more than that... if you are short at all then you get -5 points at the end of the game. The loan card is just the reminder for that point loss.
From the rules:
If a player doesn’t have enough Bridge Toll Tokens left to pay for the cost of a route, that player must take a single Loan card from the bank when claiming that route, and place it face up in front of him for the rest of the game. The player pays no Tokens (even if he could have made a partial payment), and can never reimburse this Loan.