it is oftentimes a function of what you collect as to what kind of bargains you might find. Oddball stuff can be all over the board. The general prewar stuff--mainstream sets in collector to mid-grade, can vary from table to table but I think sellers recognize they have to be more flexible if you're determined to haggle. Of course, the later in the show schedule the better the chances for a discount (and sometimes at the end of any one day), but much of the stuff has been picked over by then.
Although I agree with the notion of offering less, some sellers are just plain out of their mind high on stuff, to the point where I just walk away. This often happens with either some of the semi-scarce stuff or the regular stuff in high grade. For example, I collect m101-4s and 5s, which are not particularly scarce but with some of the ad backs they aren't garden variety cards either. A couple of years ago, a guy had Stengel in grade VG with an Indianapolis Brewing back (middle of the road back, maybe akin to Sovereign in t206) that was priced at $1750. At that time, that card on its best day should have commanded about $750. I did not want to waste my time asking the seller to take a thousand dollars or more off, and figured he would get insulted and then I would say something I might regret
He had other cards marked more than double market value and there were other sellers who priced this way too, at least on the stuff I was buying.
Bottom line and as others said, go there for other reasons, and hope you find a thing or two at about what should be paid or a few centavos less. there will be no steals, however, of that I am pretty confident.