One other thing I'll allow in my campaign, if the players are in a big city with nobles, high level wizards, etc...
The trading of magic items for consumables like potions and scrolls. Say the party has a stray +2 sword that nobody is proficient with, or is of a type of blade that nobody uses. Based on the luck of the dice, they might be able to trade that weapon for some potions and/or scrolls. I basically use the XP value of a magic item to determine its 'worth' in cases like this, and like most transactions, the players always come out having lost a little in terms of value.
In very rare cases, a noble might purchase a magic weapon from the players for money, treasure maps, and if the weapon is valuable enough, maybe a land grant or minor title.