The seller can ALWAYS negotiate the sales commission, but as the market goes up, it may be harder to get a better commission than when things were stagnant. On the other hand, as prices go up, agents may have more room to flex. Shop around, but remember...lowest price is not always best buy!!
Commission is always considered negotiable and no "standard" amount will typically be offered. Most agents do however have a percentage bottom line for which they will work for. Although sellers typically have to accept lower than they hoped for as their selling price in this market, it is important to remember that in a buyers market, you want to offer a competitive commission to attract buyers agents.