Even though they are unequals ... buyers and sellers ... the one who carries the greatest weight, has more power, tips the scale (for lack of better phrases) will vary with the particulars of each transaction?
So ... one day ... the buyer can wield the power ... and one day ... it could be the seller?
Depends on the market.
Let's take stocks for example.
If there are more sellers than buyers in the market, the price of the stock will drop until buyers can be enticed back into the market.
If there are more buyers than sellers in the market, the price will rise until sellers can be enticed back into the market.
There is also supply and demand.
Markets go through cycles of being buyer markets and seller markets.
When supply is strong and demand is weak prices drop.
When supply is weak and demand is strong prices rise.
When supply is weak and demand is weak there is equilibrium.
When supply is strong and demand is strong there is equilibrium.