Billionaire investor Bill Ackman told CNBC on Monday that it's "one of the best times in a long time to buy quality stocks."

And if you're a retail investor, you should probably do the exact opposite.

Here's why: In March 2020, Ackman went on CNBC and delivered a now-infamous rant about how "hell is coming" and everyone should sell everything. He literally said the economy was headed for collapse.

What he didn't mention during that TV appearance: he'd already positioned his fund to profit massively from the panic. Ackman had bought credit default swaps - essentially insurance that pays out when markets crash. His fund made $2.6 billion on that trade.

Then he went on TV and told everyone else to panic.

After retail investors sold in fear, Ackman closed out his hedges and went long. He bought stocks cheap from all the people he'd just scared into selling.

Now he's telling you to buy. Interesting timing.

To be clear: I'm not saying Ackman is wrong about stocks being cheap right now. With the S&P down 12% from February highs and quality companies trading at better valuations than we've seen in months, there's certainly a case for selective buying.

But when a billionaire hedge fund manager goes on TV to give free investment advice, it's worth asking: whose interests is he serving?

Ackman's fund manages $11 billion. If he's buying "quality stocks" and then telling the world about it, guess what happens? Retail money follows, prices go up, his existing positions gain value. Then he can sell into the rally that he created by going on CNBC.

It's a playbook he's run before.

The actual question for retail investors: Are stocks cheap because of temporary fear, or are we heading into a real economic downdraft from the oil shock?