No pocket listings = agents aren't even calling for new leads anymore, rising interest rate has nothing to do with an agent's ability to generate leads.If you mean multifamily apartments, 5 units and up, some of those agents will know, but not many until you are over 10 units which are more listed by only commercial brokers which I agree do understand seller finance.

Purchased and sold on the same day, it generated a $50,000 profit.

If I assume this is a rental property, your income isn't over $150k, and you're not a real estate professional then the losses the rental property generates could offset other income up to a certain amount. 

What this implies to the typical RE investor is obtaining significant cash flow is a big challenge right now and relying on other RE profit sources (such as a value add and not doing a value subtract) may be a more certain path of generating returns.  

I may try a few more "flips" just for fun, but I also have money invested in Groundfloor, Fundrise, and other income-generating investments to compare (and those ones I spend little to no time on). 

House hacking lets you live in one unit and rent out the others, which can help cover your mortgage and generate some extra income.

I think the HELOC is the way to go if you can - However after reading your post, if you are talking about a 6 figure pay day, how long would the property take to generate that 6 figures in cash flow?

The ability to generate more income for simply the cost of a building is another huge cost saving over buying an expensive commercial lot and developing it.

Here are a couple of developers you should take a look at Trion Properties, their principal Max Sharkansky posts here on BP, https://www.biggerpockets.com/blog/top-5-markets-multifamily-rentals-2019and Feldman Equities out of Tampa (3rd generation real estate family famous for having built the terminals at Chicago O'Hare) who are among the only ones opening up downtown skyrise office buildings to accredited investors.

A single property is simpler to manage, carries lower financial risk, and offers streamlined tax reporting but may generate taxable income sooner.