On: The gift of it's your problem now

[jdiez17]

In that case (using the article's analogies), you are receiving a gift (GPL/FOSS software), and choosing to give them a gift as well (money). Both transactions are 100% no strings attached.

[jopsen → jdiez17]

I bought qcad a few years ago (used it for a hobby project), I payed for it because compiling from source would have been a hassle.

Note. qcad is open source.

But yes, there is a limit for what you can charge and how far you can scale that model :)