Maybe the fact that Anna has 500+ posts in here whereas you only have 2 (the 2 right here) make MomMD members more likely to click on her link. We tend to prefer regular members over people who come here just to advertize.
Yes, I did, and I probably would not even have said anything about fertility's link if she had fully disclosed that there was something in it for her if anyone joined through her link. I believe in total honesty when asking for favors. And I could have omitted my post about reaching my goal and just kept collecting referrals, each of which gets me a $20 Amazon gift card, but I posted it.