As long as your opt-ins are legitimate and you are able to verify the number you're sending from, you shouldn't have any issues: https://www.webfx.com/blog/marketing/sms-software/

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

BiggerPockets is not in a place to verify the truth or falsity of these claims.

Verifying last 2 years of rental history very important!

Hi Natasha,During the inspection period, you'll need to verify the property’s condition and make sure it’s a good deal, especially when operating remotely.

A modest markup on material will insure they are still in business the next time you need them.From my position now as a landlord/investor I will work with labor only contractors for smaller stuff but I expect I will need to provide a certain amount of supervision during and verifying after completion.

I hope you have verified that there will be sufficient equity and that you'll be able to qualify (either DSCR or Conv) for a takeout loan or cashout refi for the hard money.

Do you verify their income?

I'd attack the credit report :) 1) lower (pay down) whatever accounts have a high utilization percentage 2) contact each of 3 major consumer credit agencies and get a free report, then dispute every hard inquiry that is *NOT* associated with an open account 3) call the credit cards you already have established and ask for a credit line increase -- often can be done online and they do not verify income, hint hint. 

Reference checks help you verify these attributes, thus reducing the risk of late payments, property damage, and eviction issues.