Question on sales prices of paintings

[Маргарита]

Hello.
has recently been interested in investing in art and viewing the results of sales of auction houses, bumping into some, in my opinion diletansky, the discrepancy, such as Aivazovsky (49 x 67 cm. "DOWNFALL OF THE SEA, 1886) goes for 6 T €!!! German auction (on this site is a picture)
or Baranov-Rossine, pictures of which went for nekolko hundreds of thousands of dollars, generally is not sold, "the rain", Oil on canvas.
57 x 73 cm (and Estimate-€ 5.000 - 8.000), same-Ilya Mashkov
(Coast of the Crimea, oil on canvas)-Estimate-€ 3.000 - 4.000-not sold out!
how you can comment? I will appreciate your answers.