What about other expenses such as lawn care, snow removal, pest control?  

Costs that I think a lot of flippers may forget to include are: interest on money in play over time, property taxes, insurance, lawn or snow maintenance, utilties, risk for vandilism, loss of doing other deals if funds are limited and tided up....and your time!!!

Here are the details on the propertyJanesville, WI4 unit; 1b/1b eachAsking Price: $100k (Also assessed at 100k)Rent: $2300 totalLandlord Costs (Gas, Water, lawn/snow): $303PITI: $832 (after Refi with loan value 98k)Vac, Maint, CapEx, Mgmt: (8,10,8,8) $782Repairs: 17 yrs SMOKE DAMAGE; new roof; new windows; Kitchen updating - Estimated: $25kMy only comp is another seller with 4 unit; 3 units with 1 bed, 1 bath; 1 efficiency; who said they were putting on market for $160k (though assessed at $115k).

I'm from the Chicago area originally, but I don't know the contractors, lawn care folks, etc in the area.

Here are the two analyses: Initial Investment Purchase Price $89,000.00 Closing Costs $2,225.00 Renovation Costs(allegedly turn key) $3,000.00 Total Investment Costs $94,225.00 Financing Costs Down Payment (%) 20.00% Down Payment ($) $17,800.00 Mortgage Balance $71,200.00 Annual Interest Rate 4.00% Loan Term (months) 360 Total Invested Capital $23,025.00 Fixed Monthly Operating Expenses P&I $339.92 Financing Charges $0.00 Administration Fees $12.50 Property Taxes $197.08 Homeowners Insurance $111.86 HOA Fees $0.00 Fixed Monthly Total Costs $661.36 Variable Monthly Operating Expenses Property Management $157.50 Advertisements/Referrals $65.63 Vacancy & Collection Losses $131.25 Capital Expenditures Replacement Fund $50.00 General Maintenance Fund $50.00 Temporary Utilities $10.00 Pest Control (Optional) $0.00 Lawn Care (Optional) $0.00 Total Variable Expenses $464.38 Total Monthly Expenses $1,125.74 Annual Operating Expenses $13,508.86 Operating Income Monthly Market Rent $1,575.00 Annual Gross Revenue $18,900.00 Monthly Profit (or Loss) $449.26 Annual Net Profit (or Loss) $5,391.14I present to you such a thorough analysis in the attempt to make sure I'm not making any glaring mistakes!

Accounting, Advertising, Cleaning, Insurance, Lawn Care/Snow Removal, Legal fees, Maintenance & Repairs, Capital Expenses, Taxes, and Utilities....and of course Mortgage?

But I am happy mowing a lawn or fixing stuff.  

I'm considering buying a couple duplexes and am curious if it is customary for the tenants to do their own lawn mowing?

Lawn care, trash, pest control ..Property management ?

HOA Fees $0.00   Lawn/Snow $0.00   Vacancy $150.40 8% Repairs $100.00   CapEx $131.60 7% Property Management $0.00   Mortgage $381.93   Total Monthly Operating Expenses $1,469.93