Bertoia side chair without mounting brackets?  

pass
I don't believe they are Knoll as I have never seen the bases welded to the seat basket.

Unless of course someone...
Unless of course someone hacked off the mounting brackets that fix to the base unit at somepoint in time - and then decided to weld the base to the seat.

Yes
They are newer production (not sure about current). I have one (and can post photos later if you want).
The glides are also the style you have shown.
The chairs should be stamped Knoll on the back of the base.

BTW
The later production chairs are not as comfortable or supportive, in my opinion. The angle of the backrest is more reclined, making it not very appropriate for dining use.

you're right woodywood (of course you are:)
Vintage Bertoia's baskets are separated from the base. If you walk into DWR you'll see differently. You'll notice that the basket is welded to the base and the wires are of heavier gauge. Plus the overall chair height is shorter than the vintage ones.
They look legit.... but look for the Knoll stamp. Knoll started stamping the chairs in the early 90's.

Pics
For your reference.

Thank you everyone for your...
Thank you everyone for your expertise!
I will ask her if the chairs are stamped. And her price went down to $250 a chair. Not bad?

In my opinion
Still kind of expensive. You can find vintage chairs for less than that. If they are in like new condition, it is an okay deal.

hmmm ok. I was hoping she wou...
hmmm ok. I was hoping she would go down to $900, especially since the chairs don't come with the seat pads, and i dont think you can tell from the pictures i posted, but there is rusting around most of the welds. And i do prefer the versions that use a thinner gauge of wire. I'm just getting antsy because im afraid someone else will scoop them up and they'll be lost to me forever!
one of my friends tells me that a furniture store by her is selling a set of 4 for $700. Will try to check those out this weekend.
thank you for the advice!

woodywood,
i checked and ...
woodywood,
i checked and they do not actually have the "knoll" stamp. I had thought that the thicker gauge chairs usually had that stamp since they are more current. do you think they may be knock-offs? the shape is convincing...but i did think they looked a bit chunky in person.

Hmm
Did you check on the rear cross-bar of the base?
That's a bit odd to me, but I haven't seen that many examples of this version myself to know whether or not all of them have the stamp. They do look authentic, in my estimation. There are no knock-offs that look like this, that I am aware of.

The woman selling them says...
The woman selling them says they aren't stamped...

She's offering them for $900 ...
She's offering them for $900 now...should i do it?

Hi
Only you can decide that! The price is okay, but you might be able to do better with a bit more perseverance.