A few days later, we collected the lease for the current tenant and came to find out that the rent is only $850, with a $150 pet fee (3 pets at $50 each).

She has no guarantee of collecting this money in the future.

I know of at least one "lender" that made a living collecting fees and never making a loans.

Should you ask the seller if all tenants are paid up, what their April, May, and June rent collection totals were, and whether any tenants are having COVID-19 related employment or income issues?

You may also need to remind them on the importance of paying rent during this time, that their rent is still due (and potentially collecting interest depending on where the property is and what's in your lease), and trying to motivate them to start paying you back now.

Are they using the rents collected to offset the debt? 

@Wesin NurThe 1% rule is just a general rule.with all things being equal, good neighborhoods will have a lower % than areas with a bad neighborhood.Good neighborhoods normally require less upkeep and may survive by collecting less than the 1%You also want to determine what the costs normally are for items such as real estate taxes and insurance.If you are in an area with a high property tax / insurance, it will likely be harder for you to cash flow at less than 1%.

If you have old windows that will break soon, I would rather retrofit them for 20% of the cost than wait a bit and have to pay a lot more while not collecting rent. 

We are collectively saving over the next 18 months.

Again, it's their responsibility to collect the rent.