different tax rates different counties?

[Anon]

for example, in california, there are dozens counties with different tax rates, to calculate the tax rates for an online shop, we need to ask the client to tell us what county he is from?

my question is

1) but i never saw the other online store asked for the counties, how do they handle the tax rates issue?

2) some people may not know what county they belongs to.

3) some people may choose the low tax rate to cheat on the online store. how do we handle that?

thanks