"Ripoff" refers to a fraudulent or unfair transaction, typically involving overcharging or deceit.
The word "swindle" is a perfect synonym as it means to cheat or deceive someone, often for financial gain.
"Mantle" (1) refers to a covering or a role and is unrelated to the concept of cheating or fraud.
"Ritzy" (2) refers to something luxurious or high-class, which has no relation to dishonesty or deception.
"Roister" (3) means to engage in noisy, boisterous activities, often in a carefree manner, but does not relate to fraudulent activities.
Conclusion:
"Swindle" is the correct synonym for "ripoff," both referring to dishonest or deceptive practices, especially in financial transactions.