I worked selling electronics in a shop from when I was 15 years old. Started there in '77. I remember selling the ZX-80, and later the ZX-81 computers by Sinclair. We didn't sell them in kit form. They used to crash a lot and you had to key in the program again. The "keyboard" had terrible tactile touch too.
I had already built the computer that came out in Radio Electronics magazine in early '78. Much more capable than the ZX80, but you had to solder it all together yourself. Chips etc onto a bare PCB, build power supply, modify b&w TV for direct video input, make an ASCII encoder for the keyboard, etc