Spider mite that common?

I bought about 15 clones off craigslist from a guy and once i got home noticed they had alot of spider mites on them.
Also bought 2 mother plants from another source and they were very clean and professional but i noticed the mothers also had a small infection of spider mites on them.

Question is.. I'm still on my first grow about 2 months in and never had an issue with spider mites. Should i call these guys back and let them know that they have mites or just drop it? Is it just that common?

I would let them know. Spidermites are a bitch.