It's definitely not a selling point for me. If I like everything else about the profile and it's just in there one time, I usually let it slide. But if he's giving the finger in other pictures, too, and generally gives a sketchy vibe, I move on.
I think some Tops do it because they think it makes them look tough. I think there are better poses to get that "service me vibe" across.
For instance, of picture of him in a relaxed manspread while sitting in a chair with an erection and big grin on his face. Give me a couple of those and an easy-going Alpha vibe in the write-up, and I'm likely at least ask your rates.