Used animal street fork, they’re asking for $100. Is $50-$75 a good offer? Also they don’t know the offset, is there a way to tell? Comes in 26mm or 15mm

I can tell you by looking at the pic, it’s a 15mm. Used forks are always a dicey buy. I’d tell him that and offer him 75. Things to check… threads on the Steer tube, any gouges, or obvious wear marks on the stem clamping portion? Check all the welds for cracks and dropouts if they’re aligned. Finally, bring a headset spacer with you and place it over the area where the stem goes. You are doing this to see if the steer tube is ovalized from previous stems. Look down at the steer tube from the top to see if there is an even gap between the spacer and the steer tube all the way around. Good luck.