It's not just a "nervous buyer".

He's currently too heavy (his planned future weight isn't really relevant), he's talking about the possibility of breaking it, he keeps changing what he wants, he's asking too many questions (which take time/money to answer) in a language the seller might be less familiar with (which adds confusion), he's seems way too picky, he thinks people are making way more from the sale than they actually would.

It's not a recipe for success.

It seems he might be someone who believes "the customer is always right" (the rally cry of unreasonable customers).

A lot of his problems would be solved by buying a bike that is available for sale in the US in a normal way (ideally, face-to-face).