Which local businesses do AI tools recommend? Answer stability, cross-tool agreement and cited sites for four trades in ten US cities

AI assistants with web search now answer questions like "Who is the best plumber in Denver?" with a short list of named businesses. We measured how stable those lists are, how much different tools agree, and which sites the answers cite. On 30 and 31 October 2026 we asked three AI tools (ChatGPT, Claude and Perplexity, each through its API with web search on) five buyer questions for each of four trades (dentists, plumbers, restaurants and accountants) in ten US cities. Each tool got each question twice. Of 1,200 planned answers, we used 1,197. Asked the same question a second time, a tool named again only 56% of the businesses it had named, on average (ChatGPT 53%, Claude 67%, Perplexity 47%), and the first business named was the same in 44% of 591 pairs of answers. On average, only 7% of the businesses named in a trade and city were named by all three tools. An answer named 6.8 businesses on average (ChatGPT 5.2, Claude 10.1, Perplexity 5.2). Almost every answer cited at least one site. Review sites and directories were among the most-cited sites in every trade, and food media and booking sites led for restaurants. This record holds the working paper and aggregate counts only: per tool, per trade, per trade and city, and the most-cited platforms, directories, review sites, media and reference sites per trade. It holds no business names, no business websites and no answer text. The results were first published, with business names, at https://aipickcheck.com/research. The study was run by AI Pick Check, which sells AI visibility audits. No business paid to appear.