I envy people who can always find a catalog, or other sellers offering the same item, or price lists, for all the items they sell.
Regarding the candy dish: I was able to find many candy dishes by Royal Crown Derby being offered, but not any in the same pattern. If they were in pristine condition, the prices being asked started at $100 and went up from there. Although ours had several flaws, it was a pretty pattern, and judging by the style it was made in the 1920's or 1930's. We let it run at $40 for about six months, then added the "Make an Offer" option. If $40 had been a fair price, someone would have bought it by then. $25 was not a ridiculously low offer, so we accepted it. What price would you put on it? Should we have discarded it because we couldn't find the correct price? Should we have just let it run forever?
Regarding the WWI gas mask: We found some being offered for $300 and more, but they were in very good condition. Ours was in terrible condition. We did the same thing, guessed at $75 and let it run for a few months. Lots of views, no buyer. Again, we added the "Make an Offer" option, $50 was not unreasonable, we accepted. What price would you put on it? Should we have discarded it because we couldn't find the correct price? Should we have just let it run forever?
Keep in mind that we have hundreds of vintage items and we're not experts in any of the categories. We don't have unlimited time to spend doing research.