The best way to find out the value of a William Newport oil painting is to take it along to a valuation day at your local auction house. You may find that the auction house organizes free valuation day to encourage you to sell your items at that establishment. This will be ideal to get an accurate value of your painting as the day will have experts who will be able to tell you whether this artist is a notable figure in the arts industry and how much they believe it is worth. However, if you believe the price the expert has given you is not as much as it should be then do not be afraid to get advice from another art expert as some may be more knowledgeable about certain artists then others.
If you are unsure of your nearest auction house then have a look in your phone book or search on the internet. The other place you could try to get a valuation is an art gallery, as many seek to buy new pieces and they may find your painting more valuable than an auction as the art galleries will know what they are after and will be an expert in this field. Contact your nearest art gallery and ask if they are looking to invest in new paintings or if they offer valuations, if they don't offer either they may well be able to recommend you to someone who will be able to help you.
If you are unsure of your nearest auction house then have a look in your phone book or search on the internet. The other place you could try to get a valuation is an art gallery, as many seek to buy new pieces and they may find your painting more valuable than an auction as the art galleries will know what they are after and will be an expert in this field. Contact your nearest art gallery and ask if they are looking to invest in new paintings or if they offer valuations, if they don't offer either they may well be able to recommend you to someone who will be able to help you.