Leveling the pool table should always be a step taken during changing the cloth. Problem is that most table mechanic's only want paid to install the cloth and not do anything extra so they can get in and out of the job. If they do anything to level the table, it's mostly just adjusting the feet of the table to level the frame, but not the slates as that can take considerably longer...and don't feel that the location owner will pay extra for that level of work....so, it don't get done. Yes, you can level a pool table with the rails on or off, only problem is...unless the rails are off the mechanic can't level the slates as they need to be leveled with the rails and bed cloth off first in order to get to the slate screws used to mount the slate so they can be backed out to level the slates as needed.
Another problem is that most table mechanic's don't really know how to level the slates, so their mind set is like...."I didn't set the table up first, so I'm not going to take the slates apart and redo them in order to make the table level"....as they're really only there to install the cloth, get paid for that work....and get out the door to the next job.
When I change the cloth on a pool table....it don't matter what kind of table it is....I ALWAYS level the slates if needed, but yes I do charge extra for that...but that service is not an option to the owner of the pool table....meaning, I already checked the level of the slates and determined before the work starts...that the level of the slates is going to have to be corrected...so, when I get into the slates to level them right, that's when I determine how much extra the bill is going to be. If the owner don't want the slates leveled...because they don't care....then I don't care either right along with the owner....and leave, because it's not right to install new cloth....and NOT level the pool table(s).
Glen