With the S&P 500 down around 17% year-to-date, savvy investors know that there will be many opportunities to buy stocks on the dip. But not every falling stock is worth buying. Some risky stocks are down for a good reason, and prudent investors are better off steering clear of them even at reduced prices.

Two stocks that look particularly concerning are Planet 13 Holdings (PLNH 11.89%) and BlackBerry (BB 0.39%). Their shares are down more than 40% in 2022 -- and despite those discounts, these are stocks you shouldn't be tempted to buy right now.

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Image source: Getty images.

1. Planet 13

Marijuana producer Planet 13 was a pot stock that I used to be excited about. The company's SuperStore dispensary located on the Las Vegas strip was conveniently located and was a popular tourist attraction; it currently has a 4-star rating on TripAdvisor, and ranks among the top 30 shopping places to visit in the city. The company did well growing its business there and maintained a market share of above 10% in Las Vegas at the end of last year.

However, with the company expanding into California and Florida, it could put a strain on its bottom line. In the Golden State, there's an excess supply of cannabis. At the same time, the Sunshine State is a hotly contested market that already boasts of big names such as Curaleaf Holdings and Trulieve Cannabis, against whom Planet 13 will have to fight for market share. Planet 13 launched a location in Orange County, CA last July, and it's still in the planning stages for its first Florida-based dispensary (it plans to have at least six locations).

All that expansion could further weigh down its bottom line. Last year, Planet 13's revenue of $119.5 million rose by an impressive 70% year-over-year. But expenses totaling $73.8 million rose at a higher rate, doubling from the $36.5 million that the company incurred in costs in 2020. The only reason the company's pre-tax loss of just under $6 billion in 2021 looked like a big improvement from the prior year, when that number was at a negative $17.9 billion, was because, in the previous year, Planet 13 booked a $16.8 billion loss related to a change in the fair value of its warrant liability. Otherwise, this past year would have looked far worse.

And with costs likely to increase, the deeper the marijuana company looks to penetrate California and Florida, the results could be worse off in the years ahead. 

2. BlackBerry

Unlike Planet 13, BlackBerry isn't growing at all. Instead, the tech company is struggling to keep its sales from falling. It reported $718 million in its most recent fiscal year for the period ending Feb. 28. That was a decline of 20% from fiscal 2021 when its top line came in at $893 million. In prior years the company had an excuse for lagging sales: It was transitioning from being a cellphone maker to providing software and enterprise solutions, including cybersecurity. But the company has been rebuilding its business for years, and there still isn't much progress to show for all the changes the company has been undergoing.

In December 2020, the stock surged after news broke that Amazon would be partnering with BlackBerry to work on a collaboration that involved collecting vehicle data using BlackBerry's vehicle data platform (IVY), which would help "create actionable insights" for automakers. A year earlier, BlackBerry announced the acquisition of artificial intelligence company Cylance. It said the move would allow BlackBerry to take "a giant step forward toward our goal of being the world's largest and most trusted AI-cybersecurity company." While there has been promising news and developments surrounding the company, the results have been underwhelming.

As a former investor, I gave up on the stock when the meme hype took off in 2021, sending BlackBerry's stock to valuations I knew it had no business being at. Today I see that not much has changed with the stock. Revenue growth continues to go in the wrong direction. For all the press releases and excitement a company may try to stir up, it's essential for investors to also factor in whether a business has strong financials backing it. If the results can't back up the company's moves, investors should be cautious about just how well management's plans are going. And at BlackBerry, they don't appear to be going well.