One of the country's biggest auto parts retailers, Advance Auto Parts (NYSE:AAP) reported higher earnings on Tuesday due to recently made bolt-on acquisitions and operating efficiencies. Though headline numbers looked appealing, not all was rosy in the company's third-quarter report. New-store growth is moving at a fast clip, but existing stores are showing weakness -- a troubling trend in the company's quest to achieve an appealing ROI. Still, the company deserves some celebration for surpassing even internal EPS estimates and setting up for substantial growth in the years to come. Here's what investors need to know about Advance Auto Parts.

Earnings recap
Sales grew 4.3% for the 4,000-location-strong retailer to $1.52 billion. Shifting down the income statement, things improved. Operating income grew 13.5% while the bottom line bumped up 17.5% to $1.42 per share -- ahead of Wall Street analyst and internal estimates. Excluding a $0.06 transaction and integration charge related to two fresh acquisitions, the company earned $1.48 per share.

The sales increase was largely a result of the integration of one of the aforementioned acquisitions -- BWP Distributors. BWP was the second-largest operator of the Carquest auto repair and parts retailer. In addition to this purchase, Advance Auto has tacked on 170 new stores in the past year, aiding the top-line growth.

For existing stores, the company saw a 2% decrease due to a weak consumer spending environment, according to management's comments. Investors should note that the comparable quarter from 2012 also represented a drop in same-store sales -- 1.8% from 2011's third quarter.

The market was unconcerned with the weak comparable-sales figures as the big story with Advance Auto centers on the two big acquisitions that put this company in the No. 1 spot for overall sales.

Focus shift
Advance Auto is betting that commercial repair is the future of the business, more than do-it-yourself auto repair. With its BWP Distributors purchase, and then the $2 billion General Parts deal in October, Advance Auto is immediately a major player in the commercial repair business.

For investors, this is an attractive long-term trend. As vehicles get more complicated, it may get more difficult for the average Joe to run into an Advance Auto and get to work under the hood. To sweeten the deal, General Parts owns Worldpac -- the No. 1 replacement parts supplier for imported vehicles. Clearly, Advance Auto is setting up to become a well-integrated service business -- much more than its current retail-centric business model. Once General Parts is fully integrated into Advance Auto, commercial repair will account for 55% of sales.

Advance Auto is realigning into the most attractively growing part of the retail auto repair business with clutch acquisitions. Same-store sales may be lagging at the current locations, and those figures will have to turn around soon before investors become discouraged with the company's capital allocation practices. Still, the long-term outlook for Advance Auto is bright and investors are wise to watch closely.