An apparaisal is a very subjective opinion and there is no right or wrong number, just one persons opinion. Sellers appriasal is unusable and could result in a different number than they buyers lender. Its the buyers lender’s responsibility to chose the appraiser.
As for a pre lisitng inspection its good to get your house in order but as a buyer would you accept the sellers inspection or would you want to have someone you hire do your own? As a buyer would you spend 400 to 500 upfront before making an offer to know what you were getting yourself into?