a retailer receives funds. and pays out funds. they are not defined as a MSB/MTS nor mixer
In FinCEN proposal it says that you can only use bitcoin through centralized exchanges that require KYC. Their definition of "CVC mixing" is totally broad:
https://fincen.gov/sites/default/files/federal_register_notices/2023-10-19/FinCEN_311MixingNPRM_FINAL.pdf, page 30.
The term “CVC mixing” means the facilitation of CVC transactions in a manner that obfuscates the source, destination, or amount involved in one or more transactions, regardless of the type of protocol or service used.
read more and have a deeper think about it
you can use funds in many ways.
it actually says if a service is defined as a CEX then it needs to be regulated.. it does not say all services need to be defined as a CEX
learn about other services not defined as a CEX.
as for mixer if you are advertising the purpose of the service is to anonymise, obfuscate, distort the lineage of the funds. they you as the advertiser are putting your service into the "mixer" category
again learn about other services not defined as a mixer
learn what the definitions do say then think about what it is not saying. and think about things in the not said category