FYI there does seem to be some sort of bug I get from time to time with my retainer where it will say she's full. However I susally don't have more than 10 items on her. After deselecting my retainer, and talking again I usually can continue dumping items on her. Assuming that's not your problem... Look above: There's good advice for profit or networking....
FFXI:Sylph - Perrin 75 Hume THF; Retired (At least from my use any way)
EVE Online:ScraperX; Retired
WAR:IronClaw- Peryn SW;SkullThrone- Grymloc BO; Retired