It depends on the breed you're wanting, if you're just wanting a few hens to roam around the garden and lay a few eggs, then ex-bats are ideal. Don't expect miracle straight away with them, they'll need a fair amount of time [a few months] to find out what being a free range hen is all about and then they'll love it.
It's also very rewarding, taking in a scraggy wreck and see it fill out into a happy, confident chicken thats out in all weathers. Watching a hen thats a year or so old take its first dust bath and see the pleasure on its face is such a huge reward. On the downside, sadly a few don't make the transition and may die from shock at such a big sudden change in their lives when health wise they are at their lowest ebb anyway.
If on the other hand you're wanting traditional rare breeds, then think firstly about breed, they all have very different characteristics, size, large fowl or bantam. Also bear in mind that certain breeds L/F are other breeds bantam size. Once you've decided on this, search around in varying places for people who breed poultry in a resaonable close distance [remember if you go for an unusual breed you'll have to travel further to find it]
Contact the breed clubs secretary for information on breeders near you or buy a poultry related magazine which has a section for breeders to advertise.
Don't be put off if the breeder won't allow you to visit their premises, this is a self protection strategy against the increasing numbers of poultry thefts.
If you are not happy with the state of the poultry, then simply walk away, otherwise you could end up in a situation where you are paying out for expensive treatments or have a dead bird on your hands.
If the bird looks lively, takes an interest in whats happening around it, then thats a fair indication of a helthy fowl. Go and see a few poultry shows for one thing it will give you an ide of breeds and for another, you'll see healthy poultry.
As for smell, theres only one reason why poultry smell bad, thats poor conditions and possibly over crowding, if so avoid, poor hygiene over crowding leads to sickness in poultry.
As for ducks, well pretty much the same applies. I would suggest you join a dedicated poultry forum, no offense intended on this excellent forum and its good members, but it covers a wide range of animals and a poultry forum specialises in poultry with some having sections on water fowl too.
Katie Thears book, starting with ducks was invaluable to myself and my husband when we first started with ducks, written in clear understandable English.
Heres some useful links for you -
Domestic waterfowl Club
The Poultry Club of Great Britain: Breeds
Sorry to go on, hope it helps Ann