Robin Hood had a whole quiver of sharp arrows. Robinhood Markets has two: its tremendous growth, and the stream of payments the U.S. online brokerage gets from financial companies that handle its customers’ trades. Both may be losing their edge, just as the company heads towards an initial public offering.

Robinhood has won over 13 million retail customers, almost 50% more than it had in mid-2019, by ripping up the old broker model of charging commissions. Instead, most of its revenue comes from so-called payment for order flow. That’s when big firms like Citadel Securities and Virtu Financial pay brokers for sending trades their way. It’s legal, and Charles Schwab and E*Trade among others do it too. Even if a broker decided to use the trading firm that pays the best rates, market rules in the United States ensure that customers always get no worse than the published price on an exchange like Nasdaq.

But politicians and regulators periodically get anxious about order-flow payments. Britain and Canada don’t allow the practice. Fidelity doesn’t accept order-flow payments for certain trades, and upstart Public eschews them altogether, instead asking customers for “tips.” Robinhood didn’t help itself when the Securities and Exchange Commission fined it $65 million for not telling customers about its reliance on such income.

There are two ways order-flow payments might come under pressure. One is regulatory intervention; the other is that Robinhood’s community of traders start to prefer brokers who make money in other ways. If order-flow payments dried up, Robinhood could try to charge commissions, but that’s tough when competitors don’t. It has other revenue lines, such as lending out securities in retail customers’ accounts to market participants like hedge funds. But lending stocks to short sellers isn’t great public relations for a brokerage aiming to democratize markets.

The surge in retail trading of stocks like GameStop will have stoked Robinhood’s growth in 2021. Yet it may not last, and the influx of new traders stuck at home in the pandemic could wane. Rivals could try to undermine a newly public Robinhood, too. Some have greater capacity for pain: Schwab effectively runs a bank on the side; E*Trade is now part of Morgan Stanley, and Fidelity is a private company.

All this makes Robinhood’s $30 billion valuation, as reported by Reuters, look steep. Say the roughly $600 million it made in order-flow payments last year represents half its revenue now, versus 80% in 2016 according to the SEC settlement. That implies $1.2 billion of revenue and a valuation that’s 25 times that, triple the multiple investors attach to Schwab or digital-payments firm Square. Founder Vlad Tenev’s disruptor status and the possibility a bigger group might buy his company will add a speculative premium. But investors in an IPO will need bravery equivalent to Robin Hood’s own.