If there is one variable that will greatly change the value of a set it is missing or replaced parts. Those sets made prior to 1870 are more valuable than later sets due to earlier sets are more ornate and have non-metal handles on knives. Earlier sets are lined with velvet or some similar material, later sets have all wood interiors. Non-metal handles are early, metal handles are later. Ivory is more desirable than composite handles.
Curved blades are earlier than straight blades.
Such a set would be one marked for a given surgeon or period and accompanied by documents to prove who the owner was or how that individual was significant. These kind of sets are rare. Usually condition will be a matter of determining the amount of rust or deterioration which has occurred to the blades or other metal parts. Heavily rusted, broken, or corroded metal is a major turn-off and greatly decreases the value. A bright and new condition set will always bring a higher price than one which is worn and heavily used.