Equipments with identifiers ending with the "_SELL" suffix get a special treatment as "sell options".
This different treatment includes:

• Different textcolor in the equipment purchase menu (similar to the already implemented "repair options")
• Price values are added to the player account instead of being subtracted.
• {Price value}-{current player credits} checkback is ignored for "sell options"(, as the price value is added).
• {Weight value}-{current free cargo space} checkback is ignored for "sell options"(, as that "sale standin" item should be removed directly after it has been awarded it to the ship. (At this point it is the responsibility of the OXP developers to remove it by script at once. This might be a source for bugs, though it worked fine in tests.)
• A given weight value in "sell options" is being used to create a "cargo space will be freed by X tons" message at the end of the description.

The current way for OXP developers to create a selling entry in the purchase menu, is to create standin items, holding the description text and linking to a script that will remove itself and the "sold" items and maybe even refunding credits. This method has proven to be powerful enough to lead to satisfying results, but it has shortcomings.

• Sale entries don't stand out as much as the fine repair option. That's a shame. :)
• The sale entry's price will always be subtracted first, what makes a satisfiable presentation of refunded credits difficult.

The changes I propose enables developers to create distinguishable "Sale" entries and still using the old method.