Consider a service which promised to scan your genome, send you the data file, and delete the sample, and their copy of the file on confirmation of your receipt. This is still vulnerable to dishonesty, but only transiently.

There's nothing logically impossible about such a service, and I'd trust it modulo actual red flags. Too bad afaik nobody's offering it. Once they're archiving their copy I just don't see how they can credibly promise privacy in the longer term.

Last I looked it didn't seem really practical to just buy your own sequencer.