If you’re going to raffle anything off, or have a contest of some sort, when you’re running it, there will be temptation to give it to your best customer, or someone you know will sing your praises to the rooftop.  

Whether you’re trying to cement a long-term contract or are choosing based on social media followers, when you do this, you’re setting a precedent for yourself that you can be bought.  

This is a thinly-veiled bribe.  If you’re not willing to play fair and abide by the randomness of chance, then don’t hold a contest.