They seem to not ask any trades from the users. No ads injected into their website, no data collection for making a profit off of it, or asking any currencies in return for this website’s service. I never used this service but that’s from what i could dig about them. Here’s what Wikipedia says about them:

"BeWelcome est servitium sociale networkingum accessibile per positionem usam disponendi domos et hospitia. Tribunal est oeconomia doni, Exercituum hospitium arguere non licet.

BeWelcome operatum est a BeVolunteer, ordinatio non prodest ordinata sicut societas voluntaria descripserunt in Rennes, Britannia, Gallia, quae ex sola voluntariis componitur. Progressio post locum, suggestum BW-rox, programmatum fons aperta et aperta est."

https://en.wikipedia.org/wiki/BeWelcome