I entered a writing contest. I'm not going to name and shame, but it appears they may have published people's work without an actual contract or payment.
Make sure you read the terms and conditions before entering a contest - in this case there were no formal terms and conditions, and from now on I'm going to be making sure there are some.
The most common scam is to claim first rights on - or even ownership of - all entries. This is often done by reputable organizations (for example, there's a reason I've never entered a National Geographic photography contest even though I consider myself a decent amateur photographer).
But now it seems you also need to watch out for ambiguities. Sometimes small writing contests are quite legitimate - I won the Enchanted Photoflare contest (and then stopped entering because I felt like I would be, in British terms, "pot hunting") and know that one's a good one.
Sometimes, they simply aren't.