I dunno. Never really had any problem with this, for a variety of reasons.
First, my time on messageboards predates the advent of digital photography. Back in the day, we usually had to pick from a small group of acceptable (usually cartoon) avatars. So I got used to avatars meaning "here's an image I like". And on a gay male messageboard with a heavy porn emphasis, one would hardly be surprised that many of us would find an image of a hot guy or porn star or good-looking body part, and say "here's an image I like".
Secondly, even with the advent of digital photography, I never have any issue confusing a hot avatar for the JUBber. Let me use Hard-Up as an example, since he posted above. When I first started noticing his posts on a regular basis, I don't ever think I thought his avatar was him. Not because I thought "no way is this smart person this hot", but because his avatar doesn't look like a self-pic. It looks like a model or actor's 8 x 10 b&w glossy. So I assumed it was a "here's an image I like" picture, not a "this is me" picture. And that's true across the board. I can't say I often play the "is that really him" game - I rarely care that much what people look like, unless I'm forming some sort of bond with them by conversing with them. But if I'm idly wondering, it's less the attractiveness of the guy in the picture, and more the quality of the shot, that sways me one way or the other. It seems most of the JUBbers who use male-but-not-me-photo avatars stick with actors, porn stars and models. Some of us might be hot, but very few of us are professional photographers.
Third point. It's rare for me to "want to see more" - I'm more turned on by hot personalities than hot body parts. But if I find a guy intriguing, and I want to know more, I just visit their JUB home page. If they're that hot guy in their avatar, they tend to have a gallery with more photos. Or they'll have a gallery of photos (or, like Hard-Up, a profile pic) that makes it clear that the avatar isn't them. (Me being me, I'll usually be more intrigued with the real photos, anyway.) And if they have no gallery, I assume the profile picture probably isn't them. Easy peasy.
I've used that Lex-looking-at-porn-on-the-floor-of-the-castle avatar almost from the get-go. It's come to mean "Lex" more than anything else. People have said they recognize and like that every time it pops on the screen. I switched it with a face pic for about a week...and people complained - they wanted the gargoyle back.

i recently swapped out my profile pic for the "horny gargoyle" drawing (it summed things up well) but my galleries are still open for business for all who care to see me in the (clothed) flesh.
The unclothed flesh? You gotta earn that.
Lex