Will take some digging into old catalogs to determine model year and correct components. From what I can see in the picture, the original stem and bar are not there. It is missing both derailleurs. Wheels look right with Shimano hubs and Mavic rims, but don't know for sure. Missing original components will ding a vintage bike value.
One more thing. Condition, condition, condition. Either a buyer is adding to display and condition is essential part of valuation, or buyer is to use as a rider, whereupon condition is not as essential, but still calculated into sell price.
Agree with Jeff. My evaluation definitely depends on it being complete (all parts installed, preferably period correct; and functioning properly). It is definitely not a "show bike" unless restored. I would check the seat post height; it may be extended past the minimum insertion mark (if no mark at least 5cm or more should be inserted; heavier rider more like 6cm to 7cm).