IRS "Dealer" and Self-Employment Tax

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I've been warned that doing too many buy/sell transactions may cause the IRS to designate me as a "real estate dealer," and force me to pay self-employment tax of 15.3% of the first $72,600 of income. I'm wondering:

1. Is that number an aggregate for all self-employed income I may have? I would assume the answer is yes, but I'm just checking

2. Can that be at all offset by earned employee income? I assume that the 15.3% is the payroll tax (maybe not) that I and my employer pay. Even if it's not, is there any way that any other taxed income can offset that $72K?

[I'll also check with a CPA, tax attorney, and all of them, of course.]