Gemini's answer didn't say the providers are unaware of these techniques or that they don't leave artifacts.
My understanding of abuse algorithms in practice is usually that there's not always _easy_ artifacts of abuse and there's usually a pool of data that indicates, but doesn't prove, abuse - which you have to tune carefully to make sure you don't false-positive-out real customers, and that usually means accepting and responding to some low-enough-to-still-be-profitable levels of abuse.
That all seems to match, from what I can tell.
Maybe someone on this platform who knows Instacart abuse systems can shed some light?