Two-tier programs exist in the minority of affiliate programs; most are simply one-tier. Referral programs beyond two-tier resemble multi-level marketing (MLM) or network marketing but are different: Multi-level marketing (MLM) or network marketing associations tend to have more complex commission requirements/qualifications than standard affiliate programs.
When promoting affiliate offers, just make sure you are fully aware of all the terms and conditions attached to your affiliate program. Some programs can be strict about how they allow you to promote their products. For example, some may limit you to banner ads and links only, while others will allow you to use paid advertising, but won't allow email marketing.
And what about joining another company's affiliate program? It's all about extra revenue. Think about your customers' needs: What other products or services would interest your site visitors? Join those affiliate programs. Affiliate programs can increase your sales with no upfront cost to you. It just takes a little time to plan your strategy and select the partners that will have the greatest impact on your business.