Respectfully, I think you're looking at this from a bad angle. You wouldn't go up to someone in the middle of a set, wearing headphones, and ask them to stop what they're doing to help you. Instead, you find someone who's finishing a set/exercise and politely say something like "hey, I'd like to try this exercise and you seem to know it well, would you mind taking a moment to give me a hand?".

I've personally done this twice this year (I genuinely wanted to learn, I'm not using it as a strategy) and it worked very well. I suppose culture plays a role but I'm in one of those countries where people don't usually socialize with strangers and it still works.

I’m typing this comment from the gym, actually. I’m on the friendlier end of the spectrum and really don’t mind helping out when someone could use some actual help. Giving a quick spot or a quick exchange of advice is common.

What I don’t enjoy is when someone ropes me into doing something for them when it becomes clear that they had other intentions for the request. It’s the ulterior motive part that can have the opposite of the intended effect.

When you realize someone asked the favor not really because they needed it but because they thought it would be an opening to get you into conversation, you start wondering what their real motive is. In this case it may be benign enough, but it’s not a great way to start a conversation

Easy one: you are about to lift something and need a spot.

"Hi, can I ask you for a spot?" - hard to argue w/premise of ask and many people would be happy to assist you and see you achieve whatever goal you have for that lift.