Free themes should work fine and are not used to try and force people to buy paid for themes.
Also, a lot of work and testing etc goes into developing themes. Frankly at $30-$40 they aren't that profitable for developers so are a bit of a labour of love anyway, certainly no one here is trying to scalp anyone.
There are no free themes for 5.7+ , the current latest version of Concrete5, floating around the net.
That is probably part of your problem. 5.6 themes WILL NOT WORK with version 5.7+. And if you're using Concrete5 5.6, there are plenty of free themes in the marketplace (although many are "dated" and non-responsive).
Sounds like you're trying to do stuff where you haven't read and understood enough of the documentation.
I've installed 5.6 and there are more choices and the pre downloaded themes actually work when you change to them. Sadly, this version is plagued with the same issue so far of being unable to install any themes from the website. I can view them all day long and as soon as I click on it, there goes the spinning wheel of death. I'll leave sit there for an hour or so and take a break. Maybe it takes that long to download a theme. I left it a half hour before and it got some, I think. Perhaps it just takes an hour or more. Patience was never my virtue.... especially when highly sleep deprived and jacked up on 4 pots of coffee since this morning.... @@
and scroll down slightly, see in Big Letters "Which Version To Use"
Don't ever give up.
If my grandpappy had given up when the Germans bombed Pearl Harbor, where would I be today?
Why I'd be eating streusel in Dusseldorf, that's where!
Not that I don't like streusel.
As are German beers.
So, come to think of it, maybe you SHOULD give up, have a beer, and come back and try in the morning.
Or maybe try a Simple Site.https://www.concrete5.org/get-started/hosting...