Something is only worth what someone has paid for it. Offering a item at a price is not the same as selling an item at a price. Someone must pay $X for ‘Y’ pottery in order to know a similar piece of ‘Y’ pottery is worth $X. To know what is similar and what is not similar is not easy.
Ebay, and other online auctions are for the most part shams, not because of the platforms, but because of the sellers. Avoid online auctions at all costs. Antiques Roadshow and other similar shows are about ratings, and ratings are driven by convincing viewers of the likelihood of having similar items in their attics. Things are valuable when they are rare. Rare means rare.
Condition is key. You can’t see condition in pictures. Often the condition as described in catalogs is somewhere between wrong to completely dishonest. You also need to know how to ascertain its condition and/or repairs. Condition and how rare it is affects value. Repairs, even good ones, usually hurt value. Seeing bad repairs makes it unattractive, and seeing good repairs makes buyers suspicious of what they may not be seeing.
Marks or lack of marks and other readily verifiable attributes on pottery pieces also affect value. The more certain you are of who and where a piece is from the better. Again, not easily done.
Values vary by collector. Value depends on what they know, or don’t know, and what type pottery they want and value.
All these factors are usually in play simultaneously.
Find a dealer or collector you trust and then trust them. Don’t try to get something of value for free. Free advice is worth every bit of its cost.