951-349-4560

These people offered me a shamelessly low-ball offer to buy my house by sending me letters in the mail. Their offer was $137,000 lower than what I had to pay for my house. They collected my home's purchase history illigally and repeatedly kept sending low-ball offers via mail. Do not contact them.

Amit wrote:

They collected my home's purchase history illigally ...

Home sales are public record, anybody can get that information.  How do you think companies like Zillow get the price history information they report?

It is legal to state any amount as an offer to buy a house (even if it is only $0.01), it is up to the owner to decide if the offer is agreeable to them.

This number is in southern California, and based on the name you state, it is probably this "Superior Homebuyers": https://www.superiorhomebuyers.com/
They are in the business of buying homes so the can flip them for a profit.
The BBB gives them an A+ rating and lists a surprisingly low 20 total complaints in the last 3 years (8 complaints closed in the last 12 months).  The BBB lists them as in business for 11 years.
In their responses to some of the complaints, they state "Our mailers also contain a website where you may opt out of receiving further communication."  You can always use that to have them stop mailing you.

I see three options you can take:
1) Ignore them.
2) If present, use that website they refer to in order to opt-out of future mailings.
3) Pick a number at least 50 times what you house is worth and tell them you will not settle for anything less than that.
4) If you feel strongly enough that this is a scam, take all the letters (including the envelopes they sent them in) to your local Post Office and tell the clerk there that you want them forwarded to the local Postal Inspector for investigation of mail fraud.