I was wondering how this thread got so bit .. not anymore ...
When dealing with the player pool at 1/2 I think it's warranted that dealers go a little out of the way to make sure things go as smooth as possible. One casino I play at has very large tables and most of the dealers announce every bet. Not so sure it's a room policy as much as it's 'accepted' to keep the games (and tips) moving along.
I would ask (almost expect) my dealers to separate a dirty stack put out for a bet. Not necessarily announce the bet, but make sure the chips are in clear view.
Now we can try to define 'dirty' ... at the risk of the wrath of psandman
Dirty, IMO, is any chip(s) 'in the middle' of other chips of a different denomination. I have no issue with greens on top of blacks or blacks on top of greens .. or even a 3rd color in there. But don't start and stop (mix) up the colors within the stack. I would even stretch this to a single chip on the bottom of a stack even though it's technically not mixed per my own definition. (Say a black on the bottom of multiple greens or reds.)
I see no reason for a non-involved player to step into this if the dealer 'fails' to do so until there may be an error happening. (Per Kelvis, I think)
To continue my typical line of thinking that dealers need to (can) do 'less' at the higher stakes I find it very typical for a player to cut out a call and then put some chips on top for a raise when pushing it out. Players at higher stakes typically would more accurately access the spot.
Long story long ... $4 on $70 is not a big deal ... chips that change the bet by much larger amounts should be made 'extra' clear if not presented as such in the initial bet motion.
Let's go crazy here and talk about Dealers who neatly stack chips when they are bet in the 'falling tower of Pisa' fashion. GL