I stumbled upon a bear that needed some repair at an antique store and it was labeled "Steiff". It was pretty pricey. Upon examining his left ear that was pinned on, I noticed that the button was missing and there wasn't a hole where it should have been. The proprietor said that not all old Steiff bears had buttons. Is that true?
The very earliest Steiff bears, perhaps 1904-1905 (I'd have to look it up), were not made with ear buttons, but the button was added very early on in Steiff history.
What's much more likely is that 1.) The button was removed or lost (if there was one), or 2.) It's not really a Steiff bear.
The early buttons, up until the 1950s or 1960s, were held in place with two little prongs, so could be removed pretty easily. Many parents recognized the choking risk and took them off, or the bears were played with and the buttons came off.
There are other ways to judge the make of a bear. It's a bit like doing detective work. You have to learn quite a lot, and then you have to put the clues together to make an informed judgment.
When Marguerite Steiff started making Bears and other animals they didn't have buttons. She only started putting buttons in their left ears because other people were copying her designs. After the first couple of years, all Steiff toys had buttons. It is their trademark.
If your Bear is from the early 1900s, it might not have a button even if it is Steiff. If the Bear is more recent, it would almost certainly have been manufactured with a button it its ear if it is truly Steiff.
Like Becky says, some people remove the buttons or, sometimes, they fall out and they don't always leave a hole where the button was.
In terms of collector's value, a Steiff Bear without a button will be valued less than an identical Bear with a button. The loss of the button could devalue the Bear by as much as 20% or even 50%. If there is a legible tush tag which does not show evidence of tampering there will be less of a devaluation than there would be if there isn't one. If you believe that the tush tag has been tampered with, all bets are off.
Let's say you have a buttonless, tagless Bear that you believe is Steiff. You could identify the Bear by the use of materials, construction technique and by looking at the design of the Bear and comparing it to known Steiffs.
While some people might try to deceive you and try to convince you that a given Bear is Steff when they know it's not, most people just don't know the difference, especially if they are not Bear collectors. Some people might look at a fine, vintage Teddy Bear and instantly assume that it is a Steiff when it could be made by a whole host of manufacturers, including Merrythought, Farnell or Herrmann. All of these Bears are valuable in their own right and could fetch a pretty penny on the collector's circuits even if they aren't genuine Steiff. However, an honest seller could fetch a good price for a Merrythought or other well-known maker's Bears if they told the truth from the beginning. A seller who tries to convince a buyer that something is worth more just because it is (supposedly) a Steiff doesn't deserve to get his price. If he truthfully told you that it is a Farnell, for instance, he could get a good price for it because Farnell is the company that made the original Bear we now call "Winnie the Pooh." (Yes, the Pooh who lives at the New York Public Library!) Who wouldn't want to have a cousin to the venerable Pooh? ;)
If you just like the Bear it is okay to buy him even if he is not a genuine Steiff but I wouldn't pay top dollar for him. I would certainly make my opinion known to the seller and I would make an offer based on whether I think the seller is naive or is trying to deceive me.
But, in any case, it sounds like a little homework is in order before you make your offer.