Can the models that are rejected by the client ,be uploaded for sale???

I can't see why not. If client rejects the work and there is no money charged, then your work belongs to you and not to anyone else and you can do whatever you want with it.

It depends on what agreement you have with your client. Generally if you want to put on sale the model, after you handed it to the client, you have to let to know that in your application. It might be that you have modelled something based on your clients IP and you don't have the rights to sell your model to someone else without explicit permission of the client.

It depends, supose George Lucas ask you to do the Millennium Falcon, and don´t like the results, even if the model is yours, the Falcon it is still the property of George, and you cannot sell other´s property.
Beeter to make an arrangement before starting to work.

Hard to say, Copyright issues are usual, this means things are not that clear.
Once I uploaded Sherlock HOlmes illustration to a print site.
I learned soon that Holmes was public domain in Europe, but not in the USA, right holders asked me to delete my illustration, but not the drawing, just the name.
At the same time, The studios that did the movie from wich I took Holmes typical design, asked me to delete the image because it also was under copyright

But I see there are thousands of models out there of cars ,many more.....which we do not have copyright of.....Not Royalty free obviously....But they are still out there.....

Well, any existing desing must belong to someone.
Chances are nobody will claim to you if you do a WWII craft model, but these designs have a designer, and they have a propietor.
Actual cars designs, as an example, they all have a designer and someone holds the rights, it´s up to you to find the limits.

There are models out there that are against any law, there is people that models copyrighted stuff, but this is the dark side, anything can happen, and then you can´t complaint.
A company can be interested in that people spreads their design even a bit out of the law, but they hold the rights and can change their mind at any moment.

But nobody can claim anything if you model true animals, plants, rocks, etc.

As stereomanik already said, it's a grey area. You can model a car after existing real thing, put the model on sale and be ok with that, but only because IP owner does not bother to chase after each case of their IP infrigement... yet. Try to search for bmw or ford models here. You probably won't find many, because those companies already actively defending their IP and others might follow sooner or later. It's up to you if you want to risk and model something for weeks just to find someday that your model was removed from sale due to infrigement claims.

ok....so I think its better to create my own models from my own designs....I guess

But what about 'editorial use only' license

Hmmm usually when someone creates a job he is supposed to pay in advance, and then even if your work doesn't suit the buyer the money will be split in parts between him and you so in everycase you are not going to work for nothing ;)
ANd for the model if it is not the intellectual property of the author and has no copyright on it, then sell it as you want :D

Why not? You can sell it, also you can sell your model if it was accepted by client if he allowed to sell it.