Is buying bitcoin with paypal legal without laundering concerns?
While I’m not an attorney, the website you describe would be considered a “money transmitter business” (MTB) which, in the US, falls under the jurisdiction of The Dept. Of Treasury FinCEN (Finacial Crimes Enforcement Network) which has regulations to prevent money laundering with strict anti-money laundering (AML) policies. You would need to register with FinCEN and comply with their regulations to legally perform such transactions on your website regarding AML/KYC (KYC is Know Your Customer). MTB laws also vary from state to state when it comes to cryptocurrency exchange for fiat money or vice versa. Just make sure to consult with a lawyer before you go live to protect yourself.