Our bank partner has a restriction that they will not accept a chargeback request if the transaction amount is less than $100. But, please let us know if you see a fraudulent transaction that's less than $100 since it will help us make our fraud prevention systems better. We also routinely refund the amount unless it happens often with your account.
The bank partner also charges us a $35 fee per chargeback request, which we pass on to our customers. The motivation behind this is to avoid frivolous chargeback requests since there's a real cost to investigating and processing each request.