a 26 will almost certainly be too big, I would guess you are a24 maybe a 25, but as has been said the spk is big, it also has the rubber toe so you can easily downsize.
but there is much more then just lentgh to consider. The spk has a very low instep, a mid width heel and wide forfoot. If your foot does not match all of these, the boots wont fit you well.
At least go put your foot in the shell before you buy any.
And never buy used boots. If your buying new off here thats good, but a used boot is not worth anything. Liners only last a short while so if the first user has done a season in them, they may not have much life left, not to mention that they will be packed out the the first foot shape.
Overall with boots spend money on them its your most inportant piece of kit