Rarely is a warranty issued on an antique or collectible itself, but a warranty in reference to the condition it was to be received in is occasionally offered. Insurance may be obtainable also, but with either, collecting on them can be hard. Some third party shipping companies may offer insurance, with inspection and packaging, and if breakage during shipment is a concern, this is an excellent option to consider. For example, if you were to purchase a vintage porcelain doll, which was sold under the assumption that it had no cracks or damage to the porcelain parts themselves, a third party shipper would inspect, pack, and ship the item. If it were to arrive broken, you know have a much easier recourse to obtain any insurance payout than if the seller just sent it and it was broken in transit.
Seller's Standings and Reputation
By dealing with companies that have good reputations, or sellers that maintain good records of accomplishment of solid deals, you will lessen any chance of a bad deal occurring in the first place. Check Ebay seller histories prior to making a bid. Enter online chat rooms that have discussions pertaining to particular sellers. Oftentimes other customers are more than willing to share both good and bad experiences to save other shoppers the same misfortunes or to point them in the direction of reputable sellers. If an online store also has a brick and mortar style store, and you have dealt with them in the past, mention this when bargaining or buying from them online. If they know you as a customer in one manner, you will often be treated as equally well when dealing with them in an alternative method.
A good seller is also willing to share information on an item. If you inquire about an item's markings or any history the seller may have about a particular item, a good seller is often more than willing to both reply and answer any questions. Evasive answers or questions just not responded too, should all be considered bad signs. Someone who in good faith wants to make a sale is willing to answer any question that is asked, if nothing more than an "I do not know".