In "yiwei"/"creer" case, Juan believes that they are going to promote him (but his belief is not very well calibrated and is likely false). yiwei/creerse asserts something about the truth value of the belief, in addition to what the belief is.
In the "doubts" case, Juan believes that they are not going to promote him. There is no assertion regarding the truth value of that belief.
The real estate market (and well, most real markets) cannot be completely explained by simple supply/demand calculations covered in a high school economics course. Nor can they be entirely explained by a highly-trained economist. There are many factors at play that complicate matters.
Why is it a fair thing to do?