Well, it depends upon where the PC's are and what item they're selling.
In large cities, most 'common' magic items gor for 50%-70% of list price (depends a bit on my mood, the effort the players put in trying to sell the stuff, the type of city they are in (is it one well known to them or not) etc. etc.)
In smaller cities, it will depend upon which specific facilities are there (a church, resident magicions, adventuring guild chapter etc.)
Also, some items are just too weird to be sold easily.
Also, when there are very specific magical items (I try to approach as many magical items as 'unique artifacts', meaning even a simple +1 sword may be the sword of Sir Whackamamy) at play, then original owners, family of owners etc. may claim the items as lost heirlooms, and although compensation for retrieving such an item may be in order, this may be more like 10-20% of list price.
Also, in many of my more deadly campaigns most players have a main PC and several cohorts / squires / apprentices / red shirts in tow, who get excess loot divvied out to them to make them more effective and bind them to the PC's.
Since buying magical items is practically impossible in most of my campaigns and the production process so time consuming and expensive, pretty much the only way that PC's can get magical stuff is by adventuring and looting it or getting stuff as rewards.
Also, a lot of cash is not a prime requisite (mostly used to buy magical items as far as I can discern on these boards) for my players to get the items they wat (they mainly use it as a way to make life easy and get mundane stuff, hire mercenaries, bribe people, raise armies and other such nonsense...)