Ebay is wrong. The same balancer fits both engines, and will also fit the 292 in some applications. The 292 balancer usually has 3 belt sheaves instead of 2, and is usually of much heavier-duty construction. Both the 230 and 250 have a 2-sheave pulley with the belt grooves machined into the outer ring of the balancer. They both fit a crankshaft snout 1 1/4" in diameter, just like a 216, 235, 261, and a lot of the V8 Chevy engines.
Since both 230 and 250 engines use the same block casting, the only way to tell the difference in the engines will be to check the stamped ID number by the distributor or measure the crankshaft stroke. A 250 has a longer stroke and the same bore size as a 230.
Jerry
