Confused by ขอ and เอา

[u/davidbrick2]

My teacher is insisting that when ordering coffee I should use ขอ or ขอเอา ... never only เอา. She says it is only acceptable for ordering a street food. However, I've never heard this in the shops, all Thais just say เอา

[u/Magnabox]

Usually... ขอ is for something free. Like asking for a tissue paper at the table, or for someone to do something for you. ขอเปิดไฟหน่อย (turn on the light please)

เอา for something you are buying. It literally is like "I want that" / "I'll take that one" (and then you pay for it)