This question is about the era of the TRS-80 Model I, ca. 1977-1979. Originally there was no software you could buy, other than BASIC itself, which was in ROM. You would write your own, or type in source code from books and magazines. Then at some point it became possible to buy software commercially on cassette tapes, such as, if I recall correctly, an editor-assembler (EDTASM) and a Star Trek game. I think these tapes came in plastic boxes the size of a large book, which you could buy at a Radio Shack store. Later still, floppy drives became available.
Is it true that Radio Shack originally had a business plan in which they would have a monopoly on software for the TRS-80? I seem to remember being told this at the time. I do think there probably was a period ca. 1978 when a Radio Shack store was effectively the only sales channel for TRS-80 software. Later (maybe 1980?), you could find ads in the back of computer magazines, and you could order games on floppy disks.
The idea of monopolizing software seems kind of goofy from today's point of view, when desktops are generic appliances, but this was a different era, and also Radio Shack did make many dumb decisions. You could also look at this as a brilliantly evil, although unsuccessful, prefiguring of the kind of walled-garden approach that Apple now takes with their phones, or of some of Microsoft's behavior.