Without a certificate you really can't trust someone selling it to you being a) internally flawless b) e color c) .4 ct weight
Since it was second hand there could be inclusions under the prongs if the jeweler didn't examine it unmounted. Also, the color is tough to judge being mounted. If the jeweler had the stone unmounted and still graded it that way, it's the jewelers internal grading system and not a reputable system like gia or ags. Their estimate of weight is just an estimate also... Unless they had it unmounted too and weighed it. You can't get exact weight without measuring unmounted.