emrik

There are a few variants of this. Most classic is to work for an actual consultancy (Accenture, ThoughtWorks et al.). That's a normal job, where you have a normal salary with the benefits etc. They will handle the sales process, and depending on the company and project you might be working with colleagues from the consultancy or you might be working as a lone contractor at the client.

The other is to be a freelancer. Then you are dependent on contracts, and you lack a lot of benefits (no guaranteed salary, no extra benefits). On the other hand, you should make a lot more money. As a freelancer, you can either work with a firm that handles the sales and account management for you, or you can try to find clients on your own. The first one has the benefit that you work with (hopefully) experienced sales people that can do the sales and contract work for you, but they can take anywhere between 10% to 30% of your rate as a commission.

Doing sales yourself is the most flexible and you likely earn the most, but I would not recommend doing it unless you have a solid contact network already. Sales is often a difficult and tedious work, and that's not always fully understood or appreciated by consultants.

I have not worked with Fiverr or Upwork, but I don't see them as a serious alternative. Too short contracts that are not paid nearly well enough. They might be nice for students that want to make a bit of extra income though.

Source: I've been a consultant and a freelancer for nearly a decade