然后如果您的航班出现任何问题，航空公司会告诉您去购票 agent 求帮助 节省下来的 $ 不值得未来可能出现的麻烦

If you even can save a few bucks.  I hardly doubt there would be "agency" tickets for US-EU routes that are cheaper than on airlines sites.

US-China MIGHT be.