at better restaurants it's usually more about what looked good at the market that day or what the chef felt like doing out of the ordinary based on availablity of ingredients, or weather, or whatever. as far as not trusting restaurants, well, i don't eat at restaurants that i don't trust. i'm not sure why anyone would. ← this has been my experience... but mostly, i think restaurants try to keep "specials" in line with the regular menu's pricing and if it is more $$ will mention it. i think the general thought is that it is tacky to mention $$ (unless the special is $$$).