I purchased a single family home in an area I knew would have no problem filling vacancies and would generate decent rent. 

Increased vacancy and expenses (common for properties I buy) would certainly impact the property value.Unfortunately, I've found that sometimes I've overpaid for a property because I overlooked some serious maintenance/capex/tenant issues, and I haven't been able to correct them in the year purchased.

Well,  the market for rentals and sales in San Diego has being hectic for the last few months, the lack of inventory is creating an increase in prices.Now in regards the rental market, with the obligation for the landlords to keep tenants even if they are not paying (COVID) this maintain the vacancy rate very low that helps the landlords to ask for a higher rate, and with a higher rent the properties will increase in value.With this situation tenants are getting backfired Is this a smart decision to keep from the government? 

At the current price and rents it seems to be a 16% cash on cash return on the $70,000 down payment but that doesn't include capital expenditure or vacancy.

Changed tenants twice but zero vacancy so far.

Based on the rental income estimate from Rentometer, I think the house would produce around $400 in cash flow after all expenses (maintenance, vacancy, CapEx…). 

(Make sure you include allowances for vacancies and loan payments)!

In my market, if a tenant is working with a realtor, you are merely a rest stop in the house hunting game.Based on my regular review of listings, if you list with a realtor you are likely to have to absorb more vacancy than others.The 2nd is until recent market changes... now we all feel like pre-pandemic Brooklyn landlords- we could rent out a garbage can.I never saw the need.

Total income less operating costs, less vacancy/loss to rent = NOI (net operating income).

Cons - If you have a vacancy, you are 100% vacant!