What pc parts can be bought used and what must be bougt as new parts?
https://pcpartpicker.com/user/AMAZING-MEGAS/saved/all parts can be bought used. LET THE BUYER BEWARE. most prefer not to buy used storage. DO NOT buy a used GPU. opt for new you never know when a GPU has been abused for coin mining.
CPU's likewise are preferred new as you can not know what it has endured.
Ram usually lasts forever and most have lifetime warranties.
I have purchased refurbished motherboards before. refurbished has been tested and still carry a warranty and is my preferred method of getting used parts.
what is your budget? have any parts now? what do you need it to do?
case, wifi, CPU if you can verify it has not been overclocked or otherwise tortured. GPU if refurbished, I would not buy used. RAM always buy in sets for compatibility sake,factory matched sets. do not try to match modules. power supplies are an always new item. SSD's are also a no go for the used market unless you can verify they are working and at the advertised capacity.
water coolers I would not suggest for used, the fluid will eventually evaporate away and cannot be refilled and are often resold right before failure. insist on new. like everything else if the motherboard works...
SSD's are often relabeled
coolers are close to failure
RAM is often falsely labeled, I have seen DDR2 being flogged ad DDR4, and of course the capacity are in megabytes.
GPU's can be tortured via parallel computing and are often resold
CPU overclocking torture...
NEW ONLY NO EXCEPTIONS:
Pretty much everything else if its working well and has not been abused and is what it says, no real reason not to go used.
hope this is helpful and what you needed