Final answer:
The share of private label grocery sales is difficult to quantify due to the market's complexity and changing consumer behaviors. Private labels are a sizable part of the industry and could be influenced by competitive dynamics and agreements among major brands, such as those seen in France's laundry detergent market.
Step-by-step explanation:
When it comes to private label grocery sales, a definitive percentage is complex to assign due to the variable nature of different markets and competitive landscapes. However, drawing from the provided context that highlights challenges in defining market shares, we can infer that private labels often hold a significant but varying portion of grocery sales. This inference is in light of instances like the proposed merger between Whole Foods Market and Wild Oats Market, where analysis by competition authorities like the Federal Trade Commission would shift from market share to the actual competition. Further complicating the estimation of private label market share is the observation that overall grocery spending did not increase during the economic downturn from 2006 to 2009, pointing to changing consumer behaviors that may affect private label sales differently across various segments.
In the broader context of market dynamics, as seen in the example from France's laundry detergent industry, where major brands controlled 90% of the market through clandestine agreements, one can deduce that private labels face stiff competition from established brands. Yet, private labels are an integral part of the grocery market, offering consumers alternatives that often lead to increased competition and variety within the industry.