https://www.dlsite.com/books/work/=/product_id/BJ254023.html
https://coolmic.me/titles/2756 (English)
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"Will You Really Sign the Contract If I Put It In...?" Training Life Insurance Saleswoman with Sex

"If you do that to me, the weird feeling is gonna come again!"
Mizuki is an insurance saleswoman with the worst performance in her company. In order to redeem herself, she was visiting a male customer introduced to her by a senior... But she never expected to be drugged by him during their meeting...
When she came to, she was in a suspicious basement, tied down to a chair, and sexually humiliated by him. With her body still bound, the man rubs and stimulates her clitoris...
"I don't like sex... but when you touch me like that..." His tongue sucks on her nipples, and his fingers stroke along the most sensitive part deep inside her...
And, after he inserts the vibrator with the stamp attached, he tells her the impossible... "Now, stamp it on the contract yourself!"

Japanese RAW: https://e-hentai.org/g/2674598/c4e5605838/