Hi,
I am sure I am the best one on Amazon MWS work as I have 7+ years experience with Amazon MWS, customer integrations, SAAS based application development.
My mostly work history is on upwork freelancer site, but I building profile here. We can talk and I can show my work to you there with Apps I have build.
Here is answers on your questions.
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1. In which of the Programming Languages are you proficient?
Answer> PHP, Python anc C#. I would prefer PHP for Amazon MWS work as I have done a lot of tasks related and code can be re-used.
2. Have you built any app for Amazon Sellers? If yes, explain its functionality in short.
Answer> Yes many, I was lease architect of euessentials.com. This is FBA repricer and profit calculator with many other features.
3. Do you have your own Amazon MWS Developer Account?
Answer> Yes I own my own development account / API keys.
4. This would be an ongoing part-time project. If selected, what would be your best per hour rate to start?
Answer> I am top rated freelancer on upwork and mostly work there, just building my profile here now, on upwork my hourly rate is 35$ and have 100+ client history there. Here I can offer 15$.
Let me know when you want to talk.
Thanks
Kalim