Everyone has unique goals, skills, and tolerance for risk that determine what strategies are most compatible and scalable for you.

Scalable definitely could be biggest advantage.

Account Closed I like apartments and how its scalability.

I've found my conversion rates are much higher with smaller more personalized letters granted it's not exactly scalable and way too time consuming, or expensive to outsource, with higher volume mailings.You may want to consider other sources for leads, such as making offers on properties on craigslist or landwatch, or could look for some tax deed properties at tax auctions. 

But once you graduate beyond your 10-conventional loan limit, doing it through asset-based lending is a bit more scalable, especially if you're investing in multiple markets. 

thanks @Rob BelandWe have been trying to streamline our system on a large scalable version. 90 days out we do a 3rd party inspection to see how they are treating the home and that report is our determination whether we want to renew their lease.

@Tysean Jackson Handwriting is a waste of time if you want to be scalable, but it's a good way to start if you're bootstrapping with very little money. 

One tenant one roof is not scalable.

What are your SCALABLE STRATEGIES for repeat real estate investing without renovations?

That will get you much of the way there, but what and where you choose to BRRRR will get you the rest of the way and could mean the difference between a scalable moderately profitable portfolio that requires more work to manage or a massively profitable one that is truly passive.