I want to know how and what type of difficulties transfers face. Is the administration of your previous institution helpful or do they get in your way? Did you experience any difficulty while transferring credits? How does the scenario change if you are an international undergrad in a university and you want to transfer to another? Is finding aid utterly impossible or close to impossible or is it just rare?
Thank you 
All of the answers to your questions HIGHLY depend on where you’re transferring from, and where you want to transfer to.
Helpfulness of previous institution depends on the school. My previous university was awful about transferring the correct credits (but it all worked out in the end).
In general, it is usually easier to transfer between in-state colleges since their credits are more easily transferrable due to similar course equivalencies/titles. So, you will find more difficulty transferring credits to out of state colleges.
Your difficulty transferring credits depends on: institution(s), number of credits, types of classes (i.e. general eds or specific electives), and discretion of admissions readers.
Aid is not utterly impossible, but few and far between. Some schools have transfer scholarships, but usually for very specific majors or student demographics. Also, if you attend a public in-state university with some sort of academic scholarship, that always helps.