Of course having a merchant account is not the only way to collect money online.
There are some transaction companies that offers the possibility to use their services and they act as fulfillment houses charging directly your customers and then paying you.
At first sight everything seems perfect but It is really better to avoid this kind of solution for the following reasons:
1. Payment delays
As it is the transaction company that collect the payments from your customer and then revert them to you, this process sometimes (...if not frequently) takes from 20 till 90 days while if you have your internet merchant account the money is generally available within 48 or even 24 hours.
2. Complicated system
The transaction company usually requires that also your customers must have an account with them, so chances are that they don't have and they don't want the hassle to set-up an account .... and you loose the sale!
3. Customers need a special software
In some cases your customers need a special software from the transaction company. Can you imagine?
4. Millions of other problems
There is always something that is not working properly, so for this reason the best way is to go and get your own merchant account solution.