If a cue butt has slight variations in amount of light underneath the forearm while rolling it on a pool table, is that bad? Does a 1/16 of an inch or a 1/32 of an inch in wobble make a difference? What is a straight butt? At what point is a cue not worth buying? I always thought that if you see a wobble when rolling it, it is warped.
In terms of play, small warpage in the butt doesn't really affect the way a cue plays. The shaft is what needs to be pretty straight for playing.
A small amount of warpage in the handle like 1/16th, is negligible and should not, in my opinion, affect the value. In fact, that's a pretty straight cue.
It's not uncommon for older cues to warp at the tenon connecting the handle to the forearm, and it will cause the forearm to rise and fall as you roll the cue. Certain tapers in the handle will make the roll out look worse than it is. If the joint is off the table when you press down and roll the handle, for example, with that type of taper you can see any tiny variation and it will exaggerate the warp.
To really see the warp in a handle, I use a flat counter and look at the gap at eye level, holding the cue by the joint and the buttcap, and slowly turn it. I look for any rise or fall in the handle, butt cap and joint. You will readily see if there is any warp whatsoever.
In an old collector cue with a wrap, if the handle is warped 1/8th or so. I'll send it out to have the handle changed.
Chris