The thing about computer repair for the general population is that they have data on the HDD or w/e that isn't secured in any way and the person fixing it can just "accidentally" look through the data which is a breach of privacy but as you said, for ordinary people they have very little options available to them. I personally wouldn't let anyone near my data let alone leave my whole system with them. The only way you can be sure your data is secure when your computer is being fixed is if you know somebody like us who can fix it and morally wouldn't look at the data. I've fixed countless computers that involves moving data to a new storage device and I am extra careful not to look at anything if I can help it.