If genome varies across cells, how much trust should we put in our SNPs since DNA we processed always come from a tissue?

Question

[mmcui0018]

Hi! I've been thinking that even two cells of the same body might contain different genome, then how much trust should we put in our SNPs since DNA we processed always come from a tissue? Please don't hesitate to share any of your opinion. Thanks!

[Vitis]

For a starter, please see this:

https://www.ncbi.nlm.nih.gov/books/NBK21894/