Not long ago I took a vintage painting to an auction house with a view to it going in a sale. It was by an artist who had been a member of a very prominent and respected group at the turn of the 19th/20th century. I could see from the online prices that the artist's paintings sold for anything from two or three thousand to zero (ie unsold). The auctioneer gave it a valuation at the lower end and explained in detail the reasons why - it was from the artist's later period, more impressionistic than his earlier works, I forget what else. Because the artist had a reputation, the auctioneer explained that his paintings would normally be bought by aficionados, but that aficionados would not place a high value on this one. Anyway, the auctioneer put a min/max valuation on it and I left it to go in the next suitable auction, with a Reserve. There was no charge for this valuation and no obligation to put it in the sale, so you might be able to find an auctioneer locally who would offer the same service.
As a footnote, the auction house actually lost the painting. This was a very reputable auction house, been in business for several generations, had prestigious purpose-built premises and held some prestigious auctions
They ended up paying me the maximum valuation and as far as I know the painting was never found, so I'll never know how much the painting could have sold for, or whether it would have sold at all.
Better take down a De Montfort print and let Mr W Casley 1882 get an airing! 
