The VFG is not in the business of doing authentications and/or appraisals. As has been mentioned in this thread, there are people who do that for a living --- our own Claire is one of them. And any kind of appraisal of this type would require having the garment in ones hands. If you truly believe this is a Chanel garment, then you will need to bite the bullet pay the money for a qualified in-person inspection and appraisal.
To describe this suit in a listing as French or “haute couture” is disingenuous since you don’t have provenance nor anything more than a feeling and a zipper. Whoever the maker, it is most definitely not haute couture.
I have an extensive collection of designer and couture vintage. I primarily focus on European houses so I have a significant number of Chanel pieces. That being said, there are several features of this suit that lead me to believe it is not a Chanel item, but I am just going to address the zipper issue.
While an Éclair zipper is a fairly good guideline that an item might have been made in France, there were many other European manufacturers there using that brand of zipper. Additionally, Éclair zippers were available to seamstresses/tailors/dressmakers. The craftsmanship of some of these people --- particularly old world Europeans --- is phenomenal. My own great aunt had a closet full of custom suits, all of which were made for her during her annual visits to Paris in the 50s and 60s.
I have at least one USA-made suit with an Éclair zipper --- I believe it carries a Bergdorf Goodman label. And yes, I have seen and owned non-Chanel suits with dual skirt zippers. It’s a fairly common couture technique --- both French and domestic. Additionally, the chain along a jacket hem was not an exclusive technique used by Chanel. I have many US and European made suits that use that very technique.
Lastly, I have to clear up one common misconception I see pretty frequently. In my decades of vintage hunting and gathering, I have seen more fake designer goods than authentic ones at “wealthy” estate sales. Just because a person has plenty of disposable income doesn’t mean they see fit to spend that money on pricey goods. I’ve also discovered incredible authentic pieces in unbelievably humble places. An item’s environment is simply not a good measure of its authenticity.