Because we generally deal with living artists only, we can usually guarantee the Provenances directly from the artist to the gallery. A provenance is the life history of the piece of artwork, and normally starts with the artist selling it, or giving it as a gift, or passing through a dealer, etc. Most of our pieces have a Provenance that comes directly from the artist to the gallery, since we are often their first entry point. When we re-sell a piece of artwork, the provenance often includes the record of that piece, exhibitions, reviews it has had, etc. Pricing artwork is a difficult science at best.
Many factors influence the price of a piece of art, but the key factor is of course demand.
The more collectors want work by an artist, the more they are willing to pay. Supply is also a strong factor. Usually emerging artists' prices are a fraction of what established well-known artists can obtain. Auction prices can vary wildly from gallery prices, depending on the bidding. Historically, oils have been more expensive than watercolors and watercolors more than drawings, and so on.