My pool table inclines in the center, and all of the balls roll to the side.
The balls are pretty old, except for the cue ball, which doesn't roll to the sides nearly as much, almost never.
EDIT: it is warped in the center.

Instructions
STEP 1: Place a carpenter's level on the felt. STEP 2: Observe any tilt. STEP 3: Have several friends lift the appropriate end of the table. STEP 4: Insert a wooden shim as necessary. STEP 5: Recheck level. STEP 6: Repeat as necessary. Tips & Warnings
If the floor is extremely tilted, consider moving the table to another location.
Don't lift the table too high or drop it.

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