Yes, they are free to sell debt. Doesn't mean it's a good idea to just get yourself in ever increasing debt.
> Is it just that French treasury bonds aren’t valued at at-least-par on the market?
That's easy to google. And that is currently:
> The France 10Y Government Bond has a -0.082% yield.
http://www.worldgovernmentbonds.com/country/france/
(Germany is -0.433% and the US is 1.289% for 10Y)
So it's not so much an issue of "being broke" but more of budget priorities