How do you decide how much to pay for an item?

[AteRiri]

For example, an item that costs RRP £675, worn once, in almost excellent condition - how do you decide how much it's worth?

Do you follow a certain formula?

No...... just whatever it's worth to you.

Not exactly, but if it's a 'Best Offer' I normally start at 20% below asking price.

Do a search for that item or similar items. Fiddle around with the search terms to see if you can get some hits. On the website version look down the side to find "Show only" and click "Sold listings". Or use the app and set the corresponding filter setting. That might give you a sense of market price on ebay.

Do advanced search for sold items & see what others paid for similar/same items. Sort by price & look for the median paid.