To a certain extent, I rely on my nose: next time you buy a "fresh" chicken from the grocery store, take a good whiff when you open the package. While I haven't bought poultry from a store for a long time, I recall that they pretty much always had a smell. I think this is part of why cooking instruction always start "rinse well in cold water and pat dry." Take a look sometime at how far out the sell-by date is on commercial poultry. We all know the level of sanitation (or not) of commercially processed poultry. If you had your duck processed by someone else, then definitely give it a good rinse when you get home.
Now, about the birds I process myself: they never have that smell, even after resting in the refrigerator for 2 days, being frozen, then being thawed, then dealt with sometime in the next couple of days. We do not have a dedicated processing area, but we do have a soapstone sink and counters and LOTS AND LOTS of clean, cold water for rinsing.
We processed a bunch of random birds (guineas, a turkey, a couple of runts) on Monday (6/13). All of the parts for stock - gizzards, hearts, feet, necks - were rinsed and put in a clean bowl with a plastic cover, and stuck in the refrigerator to wait for other parts for stock. Well, today (6/18), I finally got around to gathering up all the bits and pieces of various birds, cooked and uncooked, and remembered that I had never dealt with the bowl of stock parts.
I got them out the the refrigerator, took the lid off, completely expecting to be grossed out. Nope. They had absolutely no odor, no slime, nothin'.
So, everything into the stock pot. If it had been regular meat parts, I would have had no qualms whatsoever about cooking and eating them.
The bottom line: if you are very clean when you process, and chill thoroughly as quickly as possible, several days in the refrigerator will be fine.
Another note: most of the folks here, myself included, recommend at least one day of "resting," maybe two or more, to let the muscles relax. Otherwise you run the risk of tough meat.
Nan