To some extent, this is a judgment call, but there are some basic indicators to go by. It is basically a matter of supply and demand.

When there are more properties for sale than there are buyers to buy them, that is, supply exceeds demand, we say that's a buyer's market. Buyer's usually can get better deals when not very many buyers are competing for properties.

On the other hand, when more buyers are looking for a limited supply of properties, sellers usually can make better deals  because buyers don't have  a lot to choose from. The demand exceeds the supply. That's a seller's market.