Unless you absolutely love flipping I have often seen it is a means to generate short-term capital that you can then put into rentals (aka long term wealth). 

Fast forward three years: He’s moved out, and the property now nets him close to $1,200 a month in profit after expenses.

Income generated from within CA has to be reported in CA.

Like Kevin stated, they don't care about your business even though Im sure you are not only generating income for the area the cabin is in (generating local sales tax) but presumably you are paying taxes not only on your property but on the income you make from STR biz. 

Am I being dumb by NOT waiting, because it’s unlikely - I assume - my next deal will be as profitable (I got very lucky on this one!)

I worked them, remodeled them and made very little money and eventually sold them for little to no profit.

However, some developers are profiteering.

Again a high profit margin of 173.8%.

At the acquisition price points, and the market value of the units if you do decide to go wit a pm you’ll find yourself not being very profitable as most pm’s will charge $75 per unit min or 8-10% of gross rental income.

If there is no agreement signed and this person is just someone listed from the broker's database, I do not believe it is acceptable for the broker to collect a split in addition to the house split.If you are to consider negotiating this additional split, there is a lot to take into account here... what is the % of business that you generate on your own vs. how much your broker contributes?