What is their responsibility if the tenant they place doesn't pay?

Listen to your elders and network and attend meet and greets, but don’t pay for special attention. 

When I messaged the guest they would have to pay or leave they refused to leave.

I did withdraw from my 401k for this first property downpayment as I do not pay penalties on withdrawals and will definitely kick me into the next tax bracket for this year for overall income. 

This creates two loan payments ($100,000 of equity and $300,000 on the new mortgage).Key NumbersHome Equity Loan Interest Rate: 6%Mortgage Interest Rate: 7%Rental Income: $3,000 per monthExpenses (management, taxes, insurance, maintenance): $800 per monthIncome and ExpensesMonthly Rental Income: $3,000Monthly Expenses: $800Monthly Mortgage Payment: $2,000ExplanationThe investor earns $3,000 in rent each month.They pay $2,000 on the investment property mortgage and $800 on other expenses.This leaves $200 profit each month or $2,400 per year.However, you have to pay $6,000 interest on the equity borrowed.This leaves you with an annual loss of $3,600.While the rental property generates positive monthly income, the interest cost of borrowing the initial $100,000 results in an overall annual loss.

Issue is he is paying 750$ a month for the 3br/1ba unit.  

You go somewhere like Stamford, Norwalk, Fairfield county, etc. you will pay more/less cash flow but higher rents with higher income professionals being so close to NYC. 

You pay them 10% (of nightly rate plus any additional cleaning or pet fees) to basically manage your listing and your calendar.

Which would leave a balance on the heloc for me to pay off.

It also gives the tenant time to arrange for 1st month's rent, if they choose to not pay it along with the security deposit.