Greetings from Ireland!
If you have a Professional Selling Plan with Amazon, getting your MWS credentials is so easy that you will ask yourself afterwards why you paid someone. You have not mentioned security though. That is the real problem, in terms of protecting your account/data/money and even more importantly how Amazon's algorithms will view activity on your account in relation to their ToS.
The wrong way to do this is to give access to your log-in to a stranger on freelancer and they message you the keys. Even if they are honest and do no harm to you at this time, Amazon will see a suspicious log-in from a foreign IP address used to log in to other seller accounts. Even if they don't suspend or ban you immediately for having more than one seller account it will be a mark against you. Amazon tracks every activity on your account and they are judge, jury and executioner.
When you get the keys, all of these are available on screen:
Developer ID
AWS Access Key ID
Secret Key
Current Marketplace
Your Merchant Token
You cannot ask Amazon to change these and you never want someone you don't trust to have your AWS Access Key ID and Secret Key.
The right way to do this job is for me (or another) to guide you through Amazon while you do it. This should not be a problem to do with some preparation and then a few minutes online together. If you are interested, please message me as I have a few questions
Feel free to ask me anything.
Kind Regards
John