Regardless, I don't see anything dishonest here. I think you're focusing on the difference between what an artist gets with a commission and through a contest, without considering what the contest-holder gets:
The overall quality is likely to be lower, both due to self-selection and the lack of a guaranteed payout
There are unlikely to be sketches or alterations
The artists probably won't be particularly favoured by the contest-holder
The number of entries is in most cases undetermined
Some artists' work has little to no value to start with. I'd rather get one piece worth $20 than 20 worth $1, and that is a significant risk in such a contest.
Apparently the Concise Oxford English Dictionary differs despite being by the same publisher:
Regardless, I don't see anything dishonest here. I think you're focusing on the difference between what an artist gets with a commission and through a contest, without considering what the contest-holder gets:
Some artists' work has little to no value to start with. I'd rather get one piece worth $20 than 20 worth $1, and that is a significant risk in such a contest.