eBay and Craigslist finds

it can go very high very fast in the last few minutes.

The trick I use for eBay sales is to wait the last few minutes, evaluate the highest bid and decide for the highest I would pay for the item. Then I'd wait the last 10 seconds or even close to place my bid with the highest I am willing to shelve.

This way the prices don't go high at the beginning which is useless to everyone and I pay, if I win, only the amount I am actually willing to pay.

If I'd bit early during the auction then there's time for someone else to come and bid one more pound over me and eBay would automatically re-bid on top, thus raising the price to my highest way before the auction would end.

I use mybidder. App on Android and iOS and a plugin for Firefox.
Works well and let's you set your max bid and forget about it. I've got some silly deals using it, particularly for poorly listed things or things that end at awkward times.