I keep seeing on ebay about sellers says display doesnt work on a gpu, would it affect using hashcat or does it depend if theres more problems than "no display" on the monitor.
A graphics card whose only fault is an inability to drive a monitor is OK for use with hashcat, *however* the number of things that can cause no display, but which don't impact GPU operation, are limited.
Youre pretty much gambling on saving money and having it hopefully still work with hashcat