First of all I find it extremely unlikely that any competitors would want to 'frame' chipmixer as a scammer. That is extremely unlikely. There is a possibility that a user just wants to get free coins.

Be in a safe environment and make sure your computer is free of viruses. Chipmixer has no reason to steal your money when they've spent so much on developing and promoting this. Sweep the keys if you need to.

I find it odd that people think chipmixer is somehow less trustworthy than other services who just send the coins directly to you. If you think about it it's about exactly the same likelihood that they will scam, which is almost zero especially if dealing with small amounts.