Since we take our estates down to bare wood most of the time in the restoration process here at SPC, the sins of the previous owner (s) come to light.
Soft spots are caused by uneven burning, fast puffing, smoking the pipe whilst laid on one side, lighting that last pinch of tobacco in the bottom of the chamber instead of dumping it out, breaking in a bare wood bowl with pinches of tobacco, not resting the pipe between smokes, and God knows what else.
They look like small charred spots in the wood.
If the charred spots are over a larger area, they classify as "spider webbing" since they resemble such.
We have a post-restoration QC process in which pipes with thinned walls, burnout risks and the such, don't even make it to the website.
The ones with spots and webbing have a lot of life left in them still, but they need to be smoked with care ( I.e. don't load up a bowl of RYO and hook it up to a vacuum cleaner ). If anything happens, we have a solid return policy ......