Artifacts were incredible things. Just simply possessing one can not only give a mage a huge boost in their abilities but also various other powers that they normally wouldn't have access to.
Due to artifacts only being found in high-ranking Dungeons, the S-rank and A-rank guilds have a monopoly over them. If that was the case, how did other guilds and mages get their hands on an artifact?
There were three ways, the first was connections. Simply knowing someone in a high-ranking guild can give one benefits they normally wouldn't have access to. Although artifacts are rare, that doesn't mean all of them are powerful.
There are some that exist just for convenience rather than helping a mage in battle. Instead of keeping such artifacts, the upper guilds either pass them down to keep good relations with the guild under them or use the second method, auction.