Why would you be buying detail sets if you don't know what details you should have? My advice would basically be: Know your subject.

Somebody in China who does know the subject, and the kits of it out there, designs a print file. He then either sells it to, rents it to, or pays to have it printed (collecting from sales) by, one of the many industrial printing companies in that country. They turn out batches of them in between doing "real" work...like auto parts, for example. They just print 3D. They "don't do paper." These batches then distribute to "a crop" of Ebay sellers who pick up boxes of the things periodically and put them online. They "don't do paper," either. They just sell what came in their boxes. The original software creator would need to then also have an instruction file which he would likewise send to a printing company, who would print up batches which now have to magically be somehow united with what the 3D printer places are boxing and distributing.

It simply doesn't work like that. The money is in the part, not the instructions, so the software guy doesn't bother. He knows what he designed, why he designed it, and where it belongs on the model, and assumes that you do too if you purchased it. He's not a kit designer. They create and sell whole kits. They gather decals, instructions, kit parts, PE, boxes, etc. from various sources they've contracted with to have those things made. Then, they put it all in a nice package and put it on the market. Different business model completely. Home cottage industry printers will occasionally also spring for having instructions made because they find it helps sales. But, "China" (particularly Ebay) "don't work like that." Guy sends software to factory. Boxes of printed items are made and sent. Ebay sellers either receive batches sent, or pick them up as necessary. Nobody in that chain is in the "kit" business. They just sell parts.

Don't buy if you don't know what you're getting. Or, don't expect to be shown after purchase if you do buy. Be prepared to figure it out.