This section of the industry unfortunately is not open to a lot of people. Most Paid To Sign Up sites (PTSU's) are open to mainly members from Tier 1 and 2 countries, and even some of those are excluded. Some of the sites will allow international members to join as promoters, this means you are only able to earn by recruiting, and then earning through commissions from your down-line. So part of your research (as with all sites) is to read the Terms Of Service (TOS) to check your eligibility.
If you are able to join, then you could find the section of the industry very useful. You will get paid to subscribe, try and buy to/from various sites/companies/programs. There are offers that require no purchase or deposit, and others that require a product purchase, or paid subscription. Some of the later will require a credit card in order to complete the purchase or subscription. But you will always earn an amount greater than the initial purchase/subscription fee, providing the offer is approved.
You need to follow the terms and conditions closely when completing these offers, as there are qualifying criteria that have to be met in order for you to complete the offer successfully and qualify for payment. There are members that sign up for various products and services with no intention of continuing with subscription or purchase after they have received payment. They will also try and complete the same offer across many sites. This type of activity is completely against the spirit of this section of the industry. You should look to use these type of programs to see if there is a product or service that you are genuinely interested in, try it, then receive your payment. I look at this section of the industry as allowing me to continue with my normal purchases and interests, in testing new sites/services/products and the payment I receive is a bonus.

There is a wide range of offers and products available on many sites, but always try and record any that you participate in, if you repeat that offer at another site, only the first transaction will be approved, but if you are using this section of the industry in the same spirit it was intended with, that will not be a problem.