How much should I buy a used GTX 1080 8gb for?

[adragoncalledgeorge]

I am looking to upgrade to a GTX 1080 as cheap as possible and was thinking of getting a used one from Ebay or Gumtree. I am in the UK so I can't use Newegg or sites like that. The cheapest brand new 1080 was on sale for 399 pounds. Basically 400. I have seen some on ebay for mostly around 350-380 pounds but on Gumtree someone was selling one for 300 pounds. I don't know what is a good deal because they seem cheaper in America although it could just be due to price difference of pounds/dollars. What would be a reasonable price to buy either a GTX 1080 or GTX 1070 for? If I can't find a 1080 cheap enough I will upgrade to a used 1070. I have a GTX 1060 3gb but it's starting to struggle with playing games at Ultra settings 1080p/60fps and I want to play at higher refresh rates or higher resolutions. Any thoughts on good prices for a 1070 or 1080 used?
Many thanks in advance!

 

[mdd1963]

I have trust issues with all e-bay/used GPUs....

Only buy if you are covered for fraud or defective cards...

 

[adragoncalledgeorge]

I have bought several PC parts from ebay and sold on ebay with no issues but I understand your thinking. They don't always work.

 

[RobCrezz]

I would be going for £300 for a used 1080.