Bertoia Chair question  

the thickness has changed
The thickness of the wires has increased over the years I imagine due to the issues with them breaking. I have found this to be consistent with all the pieces including the side chairs, the diamond chairs, the bar stools and the bird chair. In my experience, the newer chairs hold up much better and rarely have broken welds or wires.

Yes
The wires have gotten thicker over time. I'm not certain if the thickness was increased just once, or at multiple times. Certainly, the current Knoll production are much thicker than vintage examples.
It would be nice to have documentation of exactly when all of the various changes to the Bertoia designs were made over time by Knoll.

Bertoia side chairs - wire gauge
I've had over 200 Bertoia side chairs and have studied them extensively in the past 6 years. I can only compare Bertoia side chairs from late 70's / early 80's to the ones you see in DWR.
Late 70's / early 80's side chairs have three different wire sizes. The perimeter wire is the largest. The next two wires on each side (4 total) are for the connection to the base are slightly smaller. All other wire on in the middle (total of 8) are the smallest. Make sure your wires are evenly spaced...that's the key to authenticity.
I've seen some horrific reproduction bases! Whew!

New question
It turns out the smaller wires that are welded to the front thicker gauge wire are welded and finished on the top side on two chairs and welded and cut on the bottom side on four of the chairs. Has anyone ever seen a difference in genuine Knoll chairs where one is welded top and one is welded bottom ?
See below images to illustrate

Liars Abroad
That's a pretty common tactic - everyone has a horror story about shipping overseas and the seller acting unscrupulously.
I would offer a refund only if they're willing to ship them back at their own expense. I would bet that they're "willing to accept them as-is, but only if you refund a chunk of the purchase price." That happens all the time.
Label-bugs are a totally different issue - equally silly and frustrating, though.
There aren't many old fakes, anyway. Bertoia chairs are a fairly recent item to enter the world of reproductions. It was too expensive to reproduce and so no one bothered. Chinese workers making repros for pennies an hour have solved that problem, but only recently.
If the chairs are old - they're almost always real. That's it.

Killian
It's quite possible. Unfortunately, I haven't kept close enough track of all the Bertoia side chairs that I've owned to recall all of the differences.
Do you know if all of the chairs are about the same age? Is the type of mounting hardware the same on all of the chairs?
Here is a recent thread with a different wire configuration.
http://www.designaddict.com/design_addict/forums/index.cfm/fuseaction/th...

Photos from the original catalogue
Here are some photos from the original auction catalogue. The chairs were all upholstered in Black which had faded to a charcoal grey. The foam in most was dry and the bottom of the chairs had broken welds and assorted issues. At least two of the chairs were labelled but they were reupholstered so long ago that I cannot remember if more had labels or not.
After reading this thread and the linked one and based on the fact the estate sale was stuffed with original Knoll furniture I am starting to think these are actually Knoll chairs, just a bit messed up when compared to the current specifications.

2nd photo
Shown are two different "generations" of chair. The chair on the left is later as indicated by the push-on glides and the different mounting hardware (a wire hairpin loop).
I wouldn't be suprised if the wire configurations are different on these two chairs.

Thanks
Thanks to everyone who helped out / offered an opinion here, I really appreciate it.
Killian.