Buying a T480/T480s in-person

Hello! I currently am in Huaqiangbei, Shenzhen. There seems to be some sellers specializing in used lenovo laptops here. Most sellers were offering about 1400CNY (~192USD) for the T480 and 1600CNY (~220USD) for the T480s, both with i5-8350, 8-16GB, 250GB ssd. I7-8550 can be obtained for 150CNY extra. All of them have either the 1080 or 1440 screen with no major price difference. Some sellers were even willing to include the 72wH battery for the T480. With that in mind, what signs or red flags should I be checking for to prevent future problems/not get scammed? I do intend to use it for some 3-4 years.