Ok, I have found some possible answers for you by reading back Luke 15 and seeing the context. I am not sure If you studied the background context here but I will briefly summarize it anyways....
The tax collectors were seen as the lowest of low to the Pharisees, because they worked with the government and they often times cheated the people and over charged them. So Christ actually made acquaintances with them and called one man out of them to be his disciple,Matthew. The Pharisees in this day were grumbling amongst themselves saying " look at Jesus he befriends these vile tax collectors".
About Luke 16:9, I will put the Actual verse from New American Standard Bible here just in case anyone wants to see.
And I tell you, make friends for yourselves by means of unrighteous mammon, so that when it fails, they whom you have favored may receive and welcome you into the everlasting habitations.
The Parable in Luke 16:1 sets the backdrop for this verse, There was a employee (debt collector) who was squandering his masters money and so some one went to tell the Master what this man was doing. And so the master fired his employee as a result. The employee was worried for his future because all he had done in his life was this work and he knew no other, and so he devised a plan...In This culture If you were good to people and excepted in their homes, you knew you would be fed for life, and so he went about to all the people he had collected his masters debts from and lowered their debts to make friends and be excepted in their homes. When his master heard of this, he actually praised the man for being so shrewd to take care of his future. And so Jesus then spoke to his disciples this verse you see here.
If we go further down we can see How Jesus defined mammon.
Luke 16:13-14 No servant is able to serve two masters; for either he will hate the one and love the other, or he will stand by and be devoted to the one and despise the other. You cannot serve God and mammon .14 Now the Pharisees, who were covetous and lovers of money, heard all these things taken together, and they began to sneer at and ridicule and scoff at Him. 15 But He said to them, “You are the ones who declare yourselves just and upright before men, but God knows your hearts. For what is exalted and highly thought of among men is detestable and abhorrent in the sight of God. 16 Until John came, there were the Law and the Prophets; since then the good news of the kingdom of God is being preached, and everyone strives violently to go in would force his own way rather than God's way into it. 17 Yet it is easier for heaven and earth to pass away than for one dot of the Law to fail and become void. Amplified Bible
hope this helps...