If they've already paid: 1. Refund PayPal payment. 2. Update shipping cost for the order. 3. Send updated invoice to buyer. If they haven't payed: Send invoice and once (three days?) have elapsed without payment, you can cancel the order without negative impact on you or buyer. I'm fairly new, but I've done both of the two things above recently. I'm sending my second overseas letter rate this week at customers request (call me crazy!) Both were small orders that I was able to reinforce while still keeping them under 3/4" thick. Also, if you ship out letter rate from PayPal, tracking is included. For international shipments, the price difference between package and letter rate have been $10-$12. I'll do it on a case by case basis for international; never for domestic. EDIT: I forgot to mention, I bought minifigures from Legoman1212's store lately. The package couldn't have arrived faster. He wrapped in bubble wrap inside a bubble mailer; top notch. Check him out! [emoji6] [emoji106]