The PC, without peripherals costs about 1280€ new over here. Assuming it is a cheap 500W PSU, a cheap 3200MHz G.Skill kit with micron 16-18-18-38 and a 500GB 970Evo
For me, peripherals do not add much value.
Razer Mamba is ~40€ used, Cloud II is about 40€ used, Webcams cost 15€ new, Keyboard is 60€ used.
But I don't want to use headphones that were used by a sweaty, stranger and touch a mouse that he used after visiting pornhub.
de.pcpartpicker.com
If this is used, the person is asking you to pay full price for the PC and giving you about 50% discount on his used keyboard, headset and mouse.
But shop prices may be very different where you are. German market is rather cheap in comparison to some regions.