fish sickness: the flips?

Free is really the only way for sarcasm to run.

I really agree with this and would also agree with the comments about skipping two or three days. I'm sure there re circumstances (growing out fry, preparing fish for breeding, etc.) where you want to feed a lot... but in most cases, just keeping fish happy... you can feed them two or three dys in a row and then skip two or three and they will be fine. Shiners are always hungry you can not use their eagerness to eat as a measure of anything.

I agree too. My best suggestion for telling people how much to feed their fish is to feed sparingly and keep an eye on the health / shape of the fish. Assume it is healthy when you got it, feed sparingly and if it begins to get noticibly thinner, sunken in belly, etc... then feed a bit more. Also watch the water quality and if it is bad feed a bit less.
I usually don't bother having someone come over to feed my fish while I am away, but have done so twice. I measured out the food into 35mm film canisters and set them on top of the aquariums and told the people coming over to just dump the contents in. Both times when I returned they told me that they couldn't believe how little food I put in, and that they were tempted to get more out of the big canister. I told them that's why I measured it out.
I can definitely relate to the shiners always being hungry too. A few years ago I tried a little experiment with my tank. I wanted to see how much food it took to fill up the cyprinid minnows so they would stop eating and I could safely add bloodworms for the darters without the minnows eating most of them. I added a big pinch of flake food, (the amount I typically gave them each day) then when all was gone added a little more and kept doing this. After 2 hours I gave up and went to bed. They did slow their feeding down, but no food ever remained for more than 2 or 3 minutes.