Promotions not understood by customer

[dolliemomma]

Is any one else having trouble lately with the promotion of offering a percent off a second item? I offer 20% off a select number of items in my store (75 items out of 300 are in this sale). This month has been terrible with customers thinking EVERYTHING is included in the second item. Even if the customer purchases two items hours apart from eachother (so obviously not on one invoice) they message me wanting to know where their 20% off the second item is (always a more expensive item too). I'm about ready to discountue the sale unless I can figure out how to  make this more clear! We used to offer $5.00 off the purchase of 3 items and we stopped that promotion because of so many customers contacting us even days later with a third purchase and wanting $5.00 off (the money off is us passing along the shipping savings if we can ship everything together because we offer free shipping).

We do have a header in our store too giving directions to use the 'cart' option and make sure all discounts are applied prior to checkout because we cannot adjust invoices.

If any one has any advice we'd love to hear it!