One of my customers is going for Hajj. He has old debts which he is not paying.

Answer

It is haraam for him to go for Hajj with the money with which he has defrauded his creditors. It is Waajib to pay the debts. There is no such thing as 'old debts' in Islam. All debts are fresh and immediately payable. This man's Hajj is not accepted. His intention is insincere. He is not going for Hajj. His true intention is to go for a tour. If the niyyat was thawaab, then he would not have committed the haraam act of abstaining from paying his debts. He will gain infinitely more thawaab for paying his debts than going for Hajj.