You’re at a conference for your industry, or it has some relation, so it’s likely that your competition is there, too.
Maybe they even have a booth in the exhibit hall or some other sort of fixed presence where their employees are gathering and speaking with current customers and prospects.
If that’s the case, take the opportunity to pick-up their collateral. It’s a great way to stay current on what they are doing and to help you come up with ideas for your business.
Also, try engaging them in conversation. Don’t hide your identity – be who you are and have a chat.
But don’t be a creeper that hangs out on the outskirts to eavesdrop on their conversations.
That’s just tacky and embarrassing.