[Enginerrrd]

They do get underage folks to try to do either "shoulder tap" operations or direct purchases from vendors. I was asked to do this once as a teenager. I refused, but not before asking a lot of questions about what I'd be doing. I can't say much about the shoulder tap operations, however, I believe there's still a couple of tells for the direct purchase attempts based on the conversations I had:

1. To ensure safety, there will be an adult (undercover cop) nearby. (This could be around the corner, or someplace sneaky, but usually they just pose as another customer.) They probably will maintain pretty close proximity to their underage undercover though.

2. They probably won't give you a fake ID, because it makes it harder to get any sort of definitive enforcement to stick. They aren't trying to catch people that are easily tricked by fake ID's so much as they are trying to catch people that are either knowingly selling booze to underage people or not making any attempt to verify.

So if someone presents a fake ID, even one that's sorta but not totally obvious, that's unlikely to be a sting operation.

3. I believe they typically will actually present ID when asked. Again this helps get charges to stick.

[cbsks]

A news article about shoulder tap operations performed by my local police department said:

Police spokesperson Sgt. Riley Harwood said that during such sting operations, the underage decoys are not made to look older with different clothes or make-up, and they’re not taught any strategies of deception. “There are no tricks,” he said, explaining if a decoy is asked for a driver’s license or ID, they hand over a valid card that shows they’re under 21 years old. “There’s no math that needs to be done,” Harwood said of the obvious differences between underage and over-21 IDs. “People just need to do their jobs.”