To me, the only time an egg smells "bad" if it is just on the verge of going bad (or has gone bad).
Egg use trivia - Does anyone know why, when cracking multiple eggs for a recipe, that one should crack each egg separately into a bowl before adding the egg to the mixing bowl?
There are 3 reasons - 2 are still valid reasons and the 3rd is due to problems from "the old days", which COULD be valid if you are raising your own eggs.
1 is to make it easier to remove any broken egg shells bits in the event you loose a piece of shell. It is easier to remove the piece from a bowl with a single egg in it than from a bowl with all the other ingredients in it.
2 is to facilitate several methods of separating the yolks from the whites.
The 3rd is to catch any "bad eggs" before they contaminate your recipe. If you are old enough you can remember hearing the term "He's a bad egg." when referring to a dishonest, irresponsible or otherwise disreputable person. That comes from the phrase "a bad egg" which refers to the cracking of an egg for use, only to find that it has "gone bad". Most folks think that means that the egg has spoiled in some way. While that is certainly true, the primary form of "bad eggs" back in the day was partially developed chicken embryos found when an egg is cracked.
This sort of "bad egg" is seldom seen with today's modern egg production methods because the mammoth egg producers never allow roosters on the facility. A hen can produce an egg without ever mating with a rooster. The egg will just never develop into a chicken, no matter how long it is incubated. So, no mating, no developing embryos.
If someone (such as our Jill) is raising chickens and are producing their own eggs, if they have a rooster running around, well, sometimes an egg gets overlooked for a day or 3 rather than being "picked fresh" from a nest and the fertilized egg could start to develop before being used, especially back before at-home refrigeration became common. So one prevention is to refrigerate any collected eggs asap.
You can sometimes determine if an egg is by candling it. The term comes from back when egg buyer would hold each egg up to a candle to see if an egg already had an embryo developing in it before paying the farmer for them. Later, with the advent of electricity and light bulbs, devices with light bulbs as the light source were developed. I remember having to candle hundreds of eggs a day back when my father bought eggs from farmers. Candling is also done when incubating eggs for hatching. It is used to determine if any of the incubating eggs have ceased developing and need to be discarded.