Is it bad etiquette to knock on doors?

[Rich Nation]

When finding vacant houses, I look up the address to find out who pays the property taxes on that address and then look that name up to determine their address for where to send my letters to. My question is: Can I just go knock on their door instead of sending the letters or is that considered intrusive?

I've owned a construction company for years and have always ran my own estimates so I'm completely comfortable with talking to people at their homes. The main difference being that I have always been invited over lol.

Thanks in advance.