Estate sales are filled with professional buyers. Things can get snapped up right in front of youDo not pick up and hold onto merchandise unless you plan on buying it. If you're interested in something but the price is out of reach, see if you can leave a bid. If it's a reasonable offer and the piece doesn't sell by the end of the sale, they may be interested. If you want to dicker, go back the second day.
Prices are usually VERY firm the first day and VERY negotiable the second day.
Call before to find out if the sale takes credit cards or checks. If you are really passionate about something, don't wait till the next day. Interview a few specialists, and go with the one you feel most comfortable with. Find out what you get for their commission. Most businesses pay for advertising, help at the sale, appraisals, sorting and displaying, conducting the sales and disposal of non-saleable items out of their commission.