What if my file gets rejected, but I beleive it is ok, can I have a dispute?
No, there is no dispute possibility.
You can only ask the community here for tips what the problem may be. For doing this, you need to post your picture and the refusal reason and other contributors will have a look into it and suggest remedies. Use therefore the keyword "contributor critique".
Because of the limited resolution with pictures posted here, you can post instead a link to a higher resolution picture. For some refusal reasons (artefacts for example) it is necessary to post an original resolution picture in good JPEG quality.
Thank you, that is the answer I was looking for.