So you're worried about these tainted coins that might be sent to you due to the mixing process eh? That's not how it works afaik. Mixing services already has their own reserve coins in their arsenal ready to be sent to the user if in case the user of the service decided to mix their coins. As simple as that, no need to worry about receiving tainted coins since mixing services got you covered and they already figured that out before you made the question into your head.
The thing about mixing is that technically, it should be considered to be an objective fact that the coins were mixed well or not... but in all reality it comes down to the fact that it's actually very
subjective.
The mere fact that with bitcoin it is technically possible for people to see that coins came from wallet A to wallet B presents a massive problem, whether you want to see it that way or not. Coinbase, or any other exchange, are technically able to shut down your account on the mere assumption that you received coins from a wallet they deem as "sketchy"... that is a major problem in the fundamentals of bitcoin, or any
decentralized currency system. Blockchain analysis will only get worse as time goes by, and if we rely on centralized sources as exchange sites, then we will see major issues with the on/off ramp to bitcoin<->fiat. Having/holding bitcoin as a store of wealth out of the fiat system is one thing, but to say that it can be used as a fungible currency is nonsense.
Sorry but your logic is down with cold or something
if you feel they can shut down your wallet because of sketchy activities then don't use their services and stop blaming bitcoin.
On topic now, what happens if I get some coins and then someone comes at my door and shoots me in the head thinking that I was the one involved in a theft or any other imaginary criminal activity?
you are probably receiving some newly generated coins because mixers like BitMixer.io are constantly renewing their reserves, yes you'll no longer find any 2 years old bitcoin in their reserve since they are not idle with their coins you know I believe they are very active trading and manipulating inputs and outputs to completely wash their vault clean.