Is it permissible for a person to perform Hajj on behalf of a deceased man who had not fulfilled the obligation, and is it permissible to accept financial compensation (the cost of Hajj) for that?

If someone dies and the Hajj al-Islam (the obligatory Hajj) was incumbent upon them, or they made a vow to perform Hajj but did not fulfill it, then it is obligatory upon their heirs to perform Hajj on their behalf or to allocate funds from their estate for someone to perform Hajj for them. It is a condition that the proxy (the one performing Hajj on behalf of the deceased) must have already performed Hajj for themselves first. There is no objection to the proxy receiving a fee for this.