Sorry, but there are two reasons why we can't grant an exemption to the 250 post rule, even for "good members" who we think might deserve it.
First, the 250 post limit is coded into the forum sales sections. People with less than that can't physically post things in the For Sale part of the forum - they're blocked. I don't know how exactly how hard it would be to write an exemption just for one specific member, but I seem to recall our coding expert grumbling about it the last time it was discussed.
Second, it would set a precedent. As soon as we granted an exemption, everyone else who wants to use the forum as a sales venue but doesn't have the prerequisite post count would jump up and down and say, "you granted that guy an exemption - why not me?". We've had threats of legal action with less provocation.
And yes, you are correct, posting a hundred "wow nice coin" comments is not an acceptable means of inflating the post count to reach the prerequisite quickly; it is a guaranteed way to make the moderators (who have to then go around cleaning up the mess) very, very annoyed with you. The mods have the power to manually lower the post counts of members who try to indulge in such practices.
Still, there are things that someone in your position can do. While you don't have the prerequisite to sell right here on the forum, you do have the prerequisite for free advertising for off-site sales. Members with over 100 posts are allowed to create a signature, which appears in every one of their posts. If you have a website of your own or are selling via some other venue, you can post a link to it in your signature. You can also post similar links in the Sale Promotion forum.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis