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I did return within 7 days. Not because of buyer's remorse but due to service center not assuring me if they will fix alignment issues.
I did trade in 2016 MS and it took 6 weeks to get my refund back. Once you trade in you will not get it back even if you return new vehicle within 7 days. Basically you will get a check for your trade in credit (if you have positive equity) and check for any down payment and Tesla will send a check directly to your financing institution.
IMHO reject delivery rather than return or you will wait for 6-8 weeks to get your refund (interest free loan to Tesla).