“guest / customer” in Japanese is 客, read kyaku, kaku (きゃく, かく). It is a Grade 3 Kyōiku kanji, taught in year 3 of Japanese elementary school, and appears in words such as 観客 (spectator).
What does 客 mean?
お客さんが来る。
Same sound, different character — the classic trap. Compare them side by side: