I'd ask him how old his shaft dowels are, how long he rests them between turns. A lot of makers keep a special stock of center cut and/or old growth dowels that are really old and really stable--not a requirement, but if you ask and he's willing to throw you a couple I think you'll be pleased. They tend to stay straighter longer regardless of climate changes. Most people never think to ask. I'd also want to know how he plans to balance/weight the cue; whether he always uses weight bolts or if the materials you prefer/want make that unnecessary. Does he core the forearms on all or some cues? When?
^Expert level questions.