[mrreality68]

VCP, Comp Look Ups, Call a Friend.

All tools to use but be aware the buyer or seller may politely decline the numbers you provide.

In addition eye appeal is a factor as many buy the card more then the grade
In addition Rarity is a key factor. If the item is rare, does not come up that often then VCP, Comp etc does not work since no track record to refer to.
If it is more common like the Goudey Ruth, the 52 Mantle etc that seem to sell all the time then Comps are easier and make more sense.

And to many what they paid is a factor. IF someone over paid they may not be willing to sell it at your "price" they may be willing to wait even extended time for the price they want/need

There is even the emotional collector out their. Many times you have to pay higher for a price if you truly want something that someone does not want to sell because they have an attachment to it