Preparation is most of the tactic
Small business sellers usually lose negotiations in the ten minutes before them, not during. The buyer, particularly a professional one, has a target, a range and an alternative written down. The seller has a price list and an intention to be reasonable. That asymmetry decides the outcome long before anyone says a number.
The fix is small and unglamorous. Before any negotiation above a threshold you set, fill in one page: target, limit, alternative, tradeable variables in cost order, and three questions to ask before commercials come up. Make it a requirement for the deal review rather than an optional exercise, since the deals that skip it are exactly the ones that need it.