The new trading week is kicking off with a pair of knocks on dot-com darling Shopify (NYSE:SHOP). Shares of the e-commerce platform provider took a 2% hit on Monday -- bucking the general market's rise -- after noted worrywart Citron Research took another shot at Shopify. The stock continued to drift lower in after-hours trading following Adobe Systems (NASDAQ:ADBE) announcing the acquisition of Shopify rival Magento. 

Adobe's $1.68 billion deal for Magento may not seem like a big deal, but it's one that could turn Shopify's small rival into a larger foe. Adobe could easily integrate Magento's offerings into its growing suite of digital products for businesses that already rely on Adobe. With some more skin in the e-commerce game, an Adobe-backed Magento can eat away at Shopify's growth.

Shopify working with apps on a smartphone and laptop.

Image source: Shopify.   

Turning the storefront into the front line 

Citron Research began writing scathing critiques about Shopify's valuation and business model late last year. The bearish thesis argued that the affiliate marketing being used in recruiting new storefronts was aggressive and bordering on illegal. Citron also called into question Shopify's customer count, a figure that has only continued to move higher with every passing quarter. 

Monday's tweet drew attention to a piece in The Wall Street Journal that Citron feels calls out what it describes as "affinity scam marketing" at Shopify.  

Citron's track record in knocking Shopify has been mixed. The stock has taken a hit in the past when Citron waxes bearish, but it has typically bounced back. Shopify stock has risen 24% since Citron's first attack seven months ago, and the gain has been even greater for investors taking advantage of the initial sell-off. 

Shopify has answered with heady growth for a company eyeing 10 figures in revenue this year. Shopify's top line surged 68% in its latest quarterly report, the latest in the e-commerce enabler's string of "beat and raise" reports. 

Guidance calls for revenue to slow to just a 52% to 55% gain in the current quarter, but we've seen Shopify toy with analysts before as it serves up lowball projections that it can barrel through with ease. We can't dismiss some of Citron's knocks. We also can't ignore the growth that Magento can experience under Adobe's wing. However, betting against Shopify has more often than not turned out to be a losing wager. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.