How accurate are the sales estimates in research tools?

Treat them as directional, not exact. Tools convert Best Sellers Rank into estimated monthly sales using category models, and independent tests put the popular suites in a reasonable range for high- and mid-rank products, with wider error in small or unusual categories. The reliable signal is relative — which product sells more than another — rather than an exact unit count. Cross-checking two tools, or reading the raw rank history, tightens the picture.