Good question :)
I found an old chair, with cobwebs on it and the wood was dry but I could sit on it, that was the main thing. It is a mahogany chair, with beautiful carvings but at the time it had faded (what I thought was velour) upholstery. I bought it for $10.00
My friend is an antiques dealer and he came and looked at the chair. It dates to Victorian times and is worth $200-$300!