To the comments above, I'd like to add one additional point that has not been raised.

There are several companies that compile historical result lists from all auctions at reputable houses. One can typically subscribe to one of these services for less than $15 for a day or about $150 a year. You can commonly do basic checks, such as whether a specific artist is in the service's database, for free. Most, maybe all, of these services cover prints as well as original works.

Practically the first thing to do for any artist that has been around a while is to see what their works have been selling for. But, with these on-board auctions providing few advance lists of what is for sale and with on-board internet access being expensive or difficult, one of the very best tools available to consumers is generally not readily available. That alone should be a major caution.