Here are some factors which may affect luthiers' willingness to set these necks:
1. There is factory finish over the joint. This finish must be separated before removing the neck. I have a little Xacto chisel (razor-blade thin and sharp; 3/8" wide) I use for this. Takes about 30 seconds.
2. Many Guild necks are laminated. Some luthiers believe there is a greater risk of separating the laminations at the heel when steaming the joint. I have not had this happen (I use steam, but only for about 45-60 seconds (three 15-20 second injection-bursts).
3. The Guild dovetail is 5º instead of the more widely used 10º. This makes it harder to get a good, fast pull-together while gluing the joint.
4. To match the factory appearance, finish must be matched, blended, sanded, and polished at the reset joint. Sometimes this is a pain in the rear due to varying factory finish color, and color-shifting from aging.
Take a look at Bryan Kimsey's comments about neck reset procedures if you want info from a paid professional who has done too many resets to count. Also look at Frank Ford's comments (frets.com).
This might interest you as well:
I just took this Guild F212XL S/N 89015 1973 neck/body joint apart and thought maybe others would like to know what it looks like, and other information. First, an observation - The Guilds I've taken apart (four from the '60s and two from the '70s) have had no dovetail shims from the factory...
letstalkguild.com