Estimating the value of a house

Hi DG Family!

I've estimated several houses and my value of the house seems to always be higher than my realtor's.

My realtor deducts for length of time listed on the market. Is this a reasonable deduction from the value? I know that this may make a seller motivated but, should she be deducting from the dollar value of the house.

Thanks for any info you can share!

Jay