When you look at the various depictions of the Mass Relays in the Mass Effect series, they appear to depict them as if they were inhabited by a crew.
Lighting certainly suggest that there is a suitable environment present in the Mass Relays for organic lifeforms.
Furthermore, when you look at other space stations that do in fact support a crew of some sort, you'll note that certainly are similarities.
However, it is never mentioned anywhere, that I could find, that Mass Relays have a crew or a population of some kind.
So, are there people living on Mass Relays? And if they do, does this not cause some problems for some story elements of the Mass Effect series?
Surely these people living there would notice and alert the council of the Geth ships / Sovereign entering the star cluster of Eden Prime (Mass Effect 1), or alerting the Alliance leaders that a massive Reaper fleet is inbound (Mass Effect 3)?