How should a multi-brand retailer structure Google Shopping or Performance Max?
By margin, then by brand. Each brand you carry has its own margin, so I group brands into tiers with custom labels in the feed and give each tier a target it can make money at. One catalog-wide campaign on a single ROAS target funds your biggest brand and quietly loses money on the thin ones.
Can an authorized dealer bid on the brand names they carry?
It depends on the dealer agreement. Many brands restrict trademark bidding, advertised prices below MAP or certain promotion wording, and the terms differ from brand to brand. I read your agreements before building anything, and the account follows the strictest rule that applies to each brand.
How do I compete when the brand and other dealers sell the same product at the same price?
On everything except price. Real stock, shipping speed, setup help, a comparison against the next model, a showroom or pickup. Those facts go onto the product page and into the ads, and the account spends where your margin can afford to win.
Why do my products show as out of stock in Google when I can sell them?
Usually because the store lets the product be ordered at zero stock, on backorder or made to order, and the feed sends the stock count instead of an availability Google accepts. The fix is in the feed rules, not the product.
What does it cost?
Three ways in. Every audit is free. One-time projects run $2,500 to $20,000, at a fixed price quoted from the audit before work starts. Monthly runs $2,500 to $8,500 a month, month-to-month: $2,500 for one ad channel and $1,500 for each add-on. At $8,500 it is the Fractional Marketing Lead seat. Ad spend is never marked up.