Yep has happened a couple of times (out of probably 50+ balls bought on ebay) to me which is why a seller who has the ball on scale pics generally gets at least $20 more from me.  Both cases ball was in great shape and price was cheap but still tagged the sellers pretty hard on feedback (wasn't worth worrying about refund).  Never know if you might drop down in weight due to injury or age.  Else might find someone who throws lighter stuff to sell or give to.  All in all though had surprisingly good luck on ebay but also noticed almost always its says seller you bought from before.  Small world for most part (dealers know their mark) and usually better to buy from someone who is listing multiple balls.  Else you get non bowlers selling one offs who tell you things like I think it weights less than 20lbs when you point out the weight is important to put on a listing lol.

I have purchased numerous balls on Ebay. Only happened to me once. Seller listed a Motiv Octane Carbon at 15lb.  I weighed it as soon as it arrived.  It was a 14lb.
Contacted Ebay.  They contacted the seller, who agreed to a refund.  They sent me a prepaid shipping label and I sent the ball back to seller.  All ended well.
Probably not much Ebay or the seller will do for any purchase after 60 days.

I have accidentally sold balls of the incorrect weight twice on eBay. Both times were errors on my part. One of them, I refunded all the guys money(including shipping) and told him to keep the ball. The other one I gave him a discount on the price.

Why the difference? The attitude of the person I was dealing with.