There is no law governing this: that is, the law does not say what does or does not go into an appraisal, or comps, or determining home value. It is up to the lender or the realtor (whomever is doing the appraisal or setting the value) to determine what factors they consider in determining fair comps, or the value of those comps, or the value of the property being appraised. That being said, since seller contributions decrease what the buyer is actually paying, it is logical and fair to reduce value by those contributions. Mathematically and financially, a $190,000 sale price where the seller contributes (or so effectively returns to the buyer) $6,000 is the same as an $184,000 price with no contributions.