Timberland boots never worn

Grey Timberland waterproof boots size 6M. Not sure how these feet, like if they run big, run small or true to size. My son grew out of them before he could get to wear them. Only flaw is the spot shown in picture. They're waterproof so I'm sure it can be cleaned with no problem, I just didn't want to use the wrong product so I left it as is.