As long as they don't position themselves explicitly, it's not possible to guarantee that they are 'benign', no matter how many anecdotal examples exist, where supposedly 'tainted' inputs were accepted.
Yeah, true. And even if they did position themselves explicitly as ignoring taint and respecting privacy, there is nothing stopping them from suddenly changing everything one day and instead becoming pro-taint, pro-surveillance, and pro-censorship. *cough* Wasabi *cough*
Although whenever I see a merchant or business using a self-hosted payment processor such as BTCPay, I immediately feel much more comfortable using them then I do with third party centralized payment processor.