Willy Martens was from the Netherlands and lived from 1856 to 1927. The originals with this theme go for 2000 to 3500, I have attached three that went for 2000, 2500 and 3500 in recent sales. Yours would be valued around the mid-range of $2500 if it is an original.
The red flag that concerns me is that oil paintings are not usually framed under glass if they are on canvas. If you have seen this same image before, it may be a print (lithograph) and not an original painting. Knapp Company of New York had publishing rights in 1919 to a piece called Ray of Sunshine that was an image of a girl with a goat, so that is a possibility. Other publishing companies bought the rights to some of his other pieces as well. In that case, a print would only be valued at $45.00.
You may have received an automated email from the site asking you to rate the question. This was premature because we we were not quite finished.
You said that you were interested in selling the piece and this (2500) would be the retail price for an original (even if under glass) if you sold it. The appraisal that an antique dealer gave is for replacement/insurance value and that number is ***** at least 2x higher than retail because there is an 'irreplaceable loss' factor.
Please add pictures of the piece by using the ADD FILES button in the lower right of your screen if you want me to keep going or do rate me if you are satisfied with the answer and my explanation about replacement value (appraisal) and retail value.
I will be glad to look at a photo later tonight (I am on east coast time) and do more research for you.
I understand. I do not have anything to do with the billing and I do not have any of your account information.