About the Mysterious Trader update...
the description (sometimes) says "a different item of the same rarity"
THIS DOES NOT WORK ON RELICS. If you end up having to get a relic that doesnt work on your build, it wont give you another shot at one that will.
Instead you get a legendary item, which can still be a better deal than a useless relic...but then the relic goes back in the pool and you could get it later.