TPG Details Grading

It depends on the rarity of the coin, and what kind of details it is.

The best bet it to try and find examples of the same thing that sold on ebay. Rough estimate for commons though cut the price in half as long as that doesn't bring it below melt value if it has a precious metal in it. If it does contain a precious metal just treat common coins like bullion at that point.

with westcoin.
One thing I would like to add is it would also depend on how much the coin increases in value with increases in grade. So if the coin is like 1928 Peace dollar which increases very little in circulated grades, a problem does not drop the value too much. For example, on Heritage an mid to high AU coin auctions for around $350 while problem examples in the same grade can still go for about $250. Now, I am assuming this is in regards to the 1892-S whose value increases exponentially with increases in grade. For these coins, a problem is going hurt the value much more than in the previous example. On Heritage, an AU-50 may sell for $1400-1500+ while a problem coin with the same amount of details could sell for between $200-1000 though there is a clustering at around $500.

Westcoin has already touched upon this but the key is eye appeal which is very subjective and that makes it difficult to say how much it would affect the value.

To me any coin labeled DETAILS (or Genuine) should not get more than 20-25% of catalog.
Truly rare coin are an exception.

I think that "questionable color" is probably the bet case scenario for a details graded coin. It's only questionable to the TPG that slabbed it, doesn't mean that the coin is absolutely, for sure, 100% artificially toned, it may just be questionable, and actually just fine! These types of details grade should bring the highest pricing in detail coins. Where as, heavy corrosion with pitting, bent, graffiti or scratched badly, etc. should bring the lowest amounts in the marketplace.

That coin could easily grade just fine on a good day at a TPG, especially with some years stored in an album allowing it to tone somewhat more. It's what I would call a good buy if you purchased it at a discount due to the details grade!