Shipping product only to have it returned because it doesn't fit can be expensive for dealers. Moreover, they can suffer a hit to their reputation if the user decides to flame them for their perceived lack of knowledge. It's likely that the dealer in this case is only being prudent by not stating as fact something that has proven to be problematic in some cases.
In your shoes, I would break down the gun and take only the barrels and a choke wrench to a nearby dealer who carries mobile choke and/or compatible 3rd party products. Try them in your actual barrels. Any doubt one way or the other will be resolved.
If you try them there and they fit, consider buying them from that retailer, even if the price is 10% more. Brick and mortar retailers are an essential part of the industry. If lowest price becomes the primary criteria, we will soon find ourselves with no place to buy ammo, no place to examine and handle new products, etc.