With an 18 you could convince Theresa to round out the total pay to 600. You can point out that while Theresa would claim to have had these textiles in holding for a while, you both know that since these textiles are in quite new and in good condition without any damage from moths, insects, or other creatures, Theresa can afford to actually hold onto them and wait until she hears about a good deal to make even more money off of these.