I believe my number eventually gets tagged as spam.

Spoofed numbers will show up as spam or scam on caller ID after some use, so if you are going to go that route you have to constantly check and change your numbers.

My VRBO is new this year and this is my second time getting scam/spam messages 

(Spam, you know ;-) Have you tried calling them instead? 

Robocallers, ringless voicemailers and spam texters can all take a long walk off a short pier.I hope the FTC starts prosecuting these creeps in earnest.

Regarding your point about your number being marked as spam.

If you provided your contact info (whether directly or via an owner contact list) you've provided permission for contact and this is not in the realm of robocalls or text messaging spam. 

However, if someone wants to take legal action against someone lives outside the US for a spam message, the costs and procedures would be different, right?

Even when it says “Likely spam”. 

If you are sending Text Messages to Arizona (Phoenix, Scottsdale, Mesa, Glendale) - which apparently investors love doing, beware that "the times they are a changin'"-----------------------------------------------------------------------------------------------------Arizona House advances bill to ensure 'Do-Not-Call' list will block spam textshttps://www.msn.com/en-us/news...Arizona lawmakers are advancing legislation that would allow residents to opt out of getting junk text messages.