A more polite way to say "No, thanks" in Japanese.
When I entered a super market in a department store in Okinawa last month, there was a staff approached me and wanted to offer me a basket for shopping. Fact is I don't need it at all so I responded "結構です" to that staff.

I soon regretted pretty much 'cause I found myself might just hurt that staff's feeling, plus I do know Japanese consider social manners pretty much seriously. So here's my question, what should I say in a more polite way in response to.

Highly appreciate in advance for any precious advices.

Question

A more polite way to say "No, thanks" in Japanese.
When I entered a super market in a department store in Okinawa last month, there was a staff approached me and wanted to offer me a basket for shopping. Fact is I don't need it at all so I responded "結構です" to that staff.

I soon regretted pretty much 'cause I found myself might just hurt that staff's feeling, plus I do know Japanese consider social manners pretty much seriously. So here's my question, what should I say in a more polite way in response to.

Highly appreciate in advance for any precious advices.

Answer

You are right in a way. Sometimes "結構です" sounds quite strong expression. You can say "ありがとうございます。でも、結構です" instead. If you add appreciative words, it sounds softer. I often use this terms.

Answer

「結構です」も十分に丁寧な表現です。
スーパーのスタッフも気分を害されたりしていないと思いますので、安心して下さい。
でも、付け加えるならば、like English、
「ご親切に有難うございます。でも、結構ですので。」と言うと、感謝しつつ断る事が出来るので、あなたの気持ちがストレートに伝わるでしょう。
ただ、我々日本人も、スーパーでそこまで丁寧な言葉遣いをすることはありません。
「有難うございます、でも、いいです。」と言いつつ、手のひらを横にwaveさせるのが、自然な反応かも知れませんね。

Answer

I think 結構です is polite enough to say "no" in Japanease .
If you want to be more polite, then you can add "お気持ちはありがたいのですが" before "結構です"
"お気持ちはありがたいのですが" means "I appriciare your concern but....."