Here is some information which most first time users or new users of a domain registrar need to know.

Many registrars offer domains for cheap and this drives in many customers.
Companies like Netfirms and other ICANN Accredited registrars get domains at much lesser base price than the price they sell them at. No one pays from their pocket, so when price seems cheap to you, it is more or less reduced profits the company is going for, with sole intention to have a customer and also in hope that the domain once registered will be kept in use subsequent years and most likely with them. So, little reduction in profit if increases volume of sale and gets them new customers, it is a good business tactic.

If a domain is put to good use, has a web site attached or is in use otherwise, chances are that it is going to be renewed the subsequent year. It may be transferred elsewhere but even then for 60 days custoemr stays with these companies and that is a good time to impress upon them with not just domain services but also expose them to wide array of other services offered through these companies. It is quite possible that customer who comes for domain services and is satisfied with same or sees other products, may purchase same.

Remember, many of the registrars, need a credit card for purchase or enroll you into paypal subscription.
Make hard note of this, because if you move domain to other place or sell the same, you MUST cancel credit card or paypal subscriptino entered into their records, otherwise it will AUTO-CHARGE you despite them not possessing the domain or you not being the owner of domain any more.
I have seen many people ignoring this and later fighting chargebacks or corresponding. So, just be careful any time you use credit card or enroll into subscriptions. Never ignore TOS, howsoever boring and long they may be.