Affiliate promotion is very profitable for those who know what you are doing.
It is important that neither you nor your affiliate partners take advantage of this process. This may cause some irritation to your site visitor. The most negative consequences being viruses or interference with tracking chains.
When your profits are at a level you are proud of, you will be able to ask for a higher commission.
You should review your affiliates are doing all the time. Getting rid of affiliates gives you a chance to make more money with a new affiliate.