I'm not sure they need to beware - DB\SCNF aren't really competing with the likes of Capitaine Train. If you buy a ticket from Paris to Lyon with CT for example - you're still getting the same SNCF train ticket and they'll get a giant chunk of that money (I have no idea what sort of referral CT get). I suppose its in these rail companies' best interests that someone puts together a nice interface for their ticket systems.

Except Capitaine Train had to go (almost? can remember the details) to court in 2009 to gain access to SOCRATE, the SNCF booking system. Capitaine is competing with Voyages SNCF and SNCF themselves. They both operate and sell tickets. (And VSC see themselves as competitors to SNCF, which is kinda schyzophrenic if you ask me).

Now that they have set a precedent, Lyria and the likes opened their booking plateforms to Capitaine.

But, still, you get odd looks if you try to exchange a CT ticket at a counter "how, that's a travel agent ticket, we don't support those" "well, yes you do, just type this booking number and you'll be able to deliver me another ticket, trust me" ;-)