Idaho law does not license travel agents. However, other states do. This is where you run into a logjam, because in each jurisdiction where you market your services, there are different licensing regulations -- which means that you could be subject to the laws of every U.S. jurisdiction where you do business.
This is a big job, though not impossible, because there are companies that do it (Travelocity, Orbitz, etc.).
That said, you may want to consider setting up your system to permit the sellers and buyers to use the system, while you simply charge for the use of the venue itself.
This is allegedly, the system used by this website, eBay, and other such "venues."
Hope this helps.
Terms and Conditions: By your continuing in this conversation with me, or by your clicking “Accept”, you are expressly agreeing to all of the following: (1) our communication is for entertainment purposes only; (2) you are not consulting me in my professional capacity as an attorney; (3) you do not seek to establish an attorney-client relationship with me, nor do I with you; (4) you will not rely on anything I say and you will obtain appropriate legal counsel via a traditional/office consultation with an attorney licensed to practice in the jurisdiction where your legal issue arises (and you may not use our communication to avoid taxpayer penalties imposed by the U.S. Dept. of Treasury); (5) by communicating with me in this public forum you are irrevocably waiving any right to privacy, confidentiality and attorney-client privilege concerning the matters discussed. You further separately declare that any payment made by you is not consideration for this contract, nor offered for any services rendered by me on your behalf, but rather is made in genuine admiration and respect for my desire to help others. If you do not agree with these terms and conditions, then you must advise me immediately.