From the tourists' perspective this little shop is a perfect cash cow (er — them as the cash cow being milked).
Tips
usage
Almost always figurative in modern Chinese. The literal sense ('fat sheep') survives mostly in restaurant names like 小肥羊 (Xiǎo Féiyáng) — the famous hot pot chain — where it's a positive descriptor of mutton.
register
Colloquial. The figurative sense — 'sucker / mark' — has a slightly cynical, predatory edge: the speaker is implying someone is about to be fleeced.
