There are many reasons why people would sell their kessils. Perhaps they had 360s and due to a tank upgrade they’re selling them for an ap700 upgrade. Or perhaps a misfortune has occurred where they have to liquidate their hobby (marriage, baby you know horrible stuff like that). Regardless of the reason, assuming the light is incapable of growing corals due to you seeing it being sold from hobbyists isn’t a sound reason to discredit the light.
People often and irrationally like to fault equipment for subpar coral grow. And I get it. We are all experts in reefing and if something isn’t going well, well dang it, it must be the lights fault or skimmer or this or that. Stepping back and meticulously Investigating more rational variables is something that is rarely done here.
I can gladly show you my wife’s tank which has a a80 growing SPS. All she has is a 20g with eheim heater, two nano koralias and a HOB filter. No algae what so ever and the rock is covered in coraline.
OP go for the deal!