This article highlights the contortions developers go through when trying to "sell" their open source product. The GPL family of open source licences let you charge for the distribution of the source code.
The oft-repeated suggestion of selling support for your open source product is probably the least attractive option to solo developers or small teams.
An alternative is the 'source only' option. It's not open source but it gives your customers the ability to adapt the source code to their circumstances.
If you are creating a B2B product (i.e. selling to profit-making businesses), the 'source only' option let's you do the one thing GPL licences forbid: charge for the source code.
For some open source advocates the term 'source only' is a dirty word. It's up to you to decide whether it suits your product.
I posted an 'Ask HN' question on this topic the other day:
Ask HN: What are you thoughts on 'source only' software products?