Wouldn't a rejection of a dispute under $50.00 result in a greater loss to the Bank so I am confused why your initial question expesses concern that you thought the limit was $50.00 only to find out it is $25.00.
As to the VISA rules Table 11-5 of Rule 11.3.4
Minimum Dispute Amount :USD $25
For Automated Fuel Dispensers the Minimum Dispute Amount is :USD $10
Also, you are thinking only about losses due to the dollar amount of the dispute. How much does you bank pay a processor to file a chargeback? What are the hard costs and the soft costs of employee time for investigating a claim for under $25.00. There is a law of diminishing return here where you may spend more in processing and human resources costs than you actually recover.
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