They must have seen you coming
see (one) coming
To view someone as being particularly gullible and thus easy to deceive, swindle, or exploit. The guys in that shop must have seen me coming, because they convinced me to buy the most expensive stuff they had. I can't believe they managed to sell you such a piece of junk. I bet they saw you coming a mile away.
They must have seen you coming.
You were really cheated. They saw you coming and decided they could cheat you easily. Andy: It cost two hundred dollars. Rachel: You paid two hundred dollars for that thing? Boy, they must have seen you coming. Bob: Do you think I paid too much for this car? It's not as good as I thought it was. Tom: It's almost a wreck. They must have seen you coming.