Sign every copy

Every photocopy you hand to a Thai office, bank or landlord (passport pages, visa stamps, work permit, house papers) is expected to carry a handwritten รับรองสำเนาถูกต้อง and your signature. Many people also write the purpose across the page, such as ใช้สำหรับเปิดบัญชีเท่านั้น ("for opening a bank account only"), with the date, so the copy can't be reused for something else, like a SIM card or loan in your name. An official may simply hand an unsigned copy back and wait. Bring your own pen, and some offices prefer blue ink because it shows the signature is original. Bring more copies than asked for: a missing signature on page three can cost you a second trip.