Very hard to provide a general answer, you're almost always going to have to look at it on a case by case basis factoring in qualities such as signature value, rarity and the extent of the damage.
I am sure you already know the answer to this question. Unless you are talking about a unique collectible, condition is very important
Of course I understand it loses value, my question is in your experience how much? Let’s say a signature baseball is worth 100$; it gets water damaged smudge a little. You drop your offer to $50, $60,$70 ect just asking for range and ideas of worth not quotes I know it’s very much situational
It's a case by case consideration. Depending on the rarity of the signature even the slightest damage, especially to the signature, can dramatically reduce the value. Actually, seeing the item in question would make it far easier to evaluate.
I agree that it’s on a very case-by-case basis hinging on value and supply.
For example, a Babe Ruth signed photo with some edge wearing and creases is not going to be affected much by minor condition issues. However, a Mickey Mantle signed photo with the slightest bit of damage will suffer a drastic reduction in value. The reason is that mint condition Mantle photos are in good supply. Why settle for a clunker when so many perfect ones exist?
Trump smudged. As an example doubt I bid, as there are different autographs I’d prefer
Trump is going to be a very accessible and affordable autograph for many reasons. No reason to settle for a damaged example of his signature