There is no way to find the reason that the purchase history was exported in UTF-8 format, since they said they didn't know. But anyway if it's true they didn't touch data at all, we don't need to put convert system on the purchase history.
I want you to confirm following two points to them.
1) We're afraid that if customer information will be exported in ANSI format, Thai character will be garbled. So that we want to have sample customer information file that has Thai charactors. Could you ask them to send some sample customer information file?
2) I will attach some our purchase history in UTF-8. We want them to check if it's be able to import in their system.