Big Differences From NGC List Prices?

In my brief experiences here over the last few months I've found that most all of the local dealers either use the grey sheet completely( starting at the ask and settling for the bid - at a minimum ) which is not that far off of the NGC/Numismatics price lists. Same with ebay and online shops as they all seem to be in that same ballpark for most coins ( the major differences being grading "difference of opinons" in my experiences so far ).

Yet many on this site keep insisting there is no "norm" or even approximation - as if no one can use anything - which is kind of ridiculous if you ask me as EVERYONE uses SOME REFERENCE point!!

So my question is which coins do you find "locally or nationally" - ebay and online shops being what I call national outlets, to vary most from grey sheet approximations?

As an example, I have been able to pick up $10 gold Indian coins at well below such "list prices" locally at coin shows and mom-and-pop shops. Only found one bargain in a lot of looking "nationally" - by comparison. Gold, in general, seems marked up the most on such sites/lists.

I've also noticed a fair amount of extra "mark-up" on ebay for some AU grade coins. Below AU and above (MS) seem a lot more plentiful and more likely to approximate NGC prices, say +/- 10%, but AU can often go 20% or more above. I guess a lot of buyers are targeting those grades more as they seem to garner a premium comparatively - in the coins I've been shopping for at least.

Locally, most shops also have either LOW GRADE F2/AG3-VF20 coins much more than higher quality. I think its because they can't afford high volumes of higher end coins sitting around, and so many of their customers are looking low end - or bullion only - these days it doesn't pay to have a lot of AU and MS inventory for most of them! Several have told me that "fellow dealers" come through every 6-months and "clean them out" of any higher quality coins they have in inventory. Not sure if those dealers then sell online ( the shops telling me this don't use ebay and don't have a site or web presence at all ) or just use the coins for sale in their shops or at shows or what.

Which coins have you found to differ the most?