Three ideas are often mixed up. The colour model is the method: RGB mixes light, CMYK mixes ink, greyscale stores brightness only. The colour space fixes which real colours the numbers stand for, so sRGB and Adobe RGB are two RGB spaces. The profile is the tag in the file that names the space. A rule that asks for RGB rules out CMYK; a rule that asks for sRGB is stricter.
Each space has a gamut, the set of colours it can hold. Some product colours lie outside sRGB: neon yellow and orange, some deep teals and saturated violets. Converting to sRGB moves them to the nearest colour it has, so such a product can look duller online whatever is done. Checking these colours against the item after conversion, and saying so in the listing where the difference is clear, avoids a surprise at delivery.
Files can also arrive in modes that are not RGB at all. A black-and-white photo saved in greyscale mode, an image from an old GIF in indexed colour, or a file in Lab from a professional editor can be refused by an upload form that expects RGB, or shown with shifted tones. Converting the mode to RGB, then the space to sRGB, prepares any of them for a listing.