Yes, a cash offer is always stronger.

Also, there is something about "showing up at their door" that makes the relationship going forward much stronger. 

That's all I'd do.This approach forces them to put their best foot forward because they will be competing with other buyers, and maybe you'll get multiple offers again (and higher than theirs or stronger buyers).It also prevents you from becoming their personal home designer/contractor.

In the near-to-mid term, these markets are unlikely to recovery like some of the stronger rental markets on the east side of the city.Your best bet at selling these units will be to the renter themselves or in a large portfolio, like @Marc Ramsay is looking to do.

But I keep losing to other buyers because they most likely have a stronger position in regards to down payment.

The construction is required to be built to the same codes as site built homes, but in reality it's actually built stronger because it has to withstand a road trip on the back of a flatbed.

You essentially the freedom to choose your risk profile for insurance on your property instead of being mandated by a bank.Lastly, you can generally get a slightly lower overall purchase price in more competitive markets as a cash offer is always viewed as stronger and owners would be more likely to accept.  

The fear of what could happen is always going to be there, but pushing through that is how we get stronger.

I had a deal kind of like that and they wanted to get full info on the tenant and asked if I could get them to sign a new, "stronger" agreement and after the background check it went on fine. 

Is this question a thought at making the offer appear stronger?