It is important to evaluate what we do and do not like about a work of art in order to appreciate it. Every artist puts a monetary value on his work according to what he thinks the marketplace will bear. If you enjoy the work enough to pay that price, that's the correct price to pay. There is no way to predict the future value of a work of art. This is not the standard one should use when buying art.
Art is for self-pleasure.
If, in the future, the work can be sold for more than its original price, that is an unexpected benefit, and means only that someone else values the artwork at a greater market price. If the work is a print or reproduction it will be signed and numbered with the total number of impressions in the edition and the order in which the impression is signed. Before oil paints were manufactured commercially, painters mixed their own pigments pulverized from plants, animals, and colored stones. The pigment was diluted with turpentine or linseed oil. When applied with a palette knife the pigment is not diluted.