I don't think this is much needed. Id go for something tlike this:
You are putting a char on trade. He have equipped 7 bis items. You can declare minimum number of items that someone can buy.
For example, I have char with 7 bis. I delcare minimum 3. That means buyer can get this char with 3 bis items he choose for 72 coins, 4 bis items for ~90, 5 bis items for ~110 and go on till 7 items. If I have bis trinkets, weapon, chest, head, shoulders, pants he can just choose trinkets+weapon, pay 72 coins for it (normal price for now) and the rest is destroyed.
This could prevent spam on global chat in game, where a lot of people type something like this:
WTS druid 7 bis, can unequip few items if You want, whisper me!