It is very easy to exchange money in Krakow - but the rates can vary a lot.
When exchanging from GBP to PLN, if the official rate is 5.9 (5.9PLN for 1GBP), you might see some money exchange offices (they are named "Kantor" in Poland) display a rate of 6.1. This will be when exchanging from PLN into GBP - and it is a scam. If the exchange office only displays one rate (not the buy and sell rates) for each currency outside its shop then generally it will not be a good rate. They will advertise the rate for converting from PLN to your currency (they can use a higher number for this, as they divide this number).
Just always confirm with them first how much PLN you will get for your currency.
The best way to find the best rates is to use this money exchange comparison website for Krakow. Most of the money exchange offices listed are within 5 min walking distance of the main square.
Don't exchange money at the airport, or at any exchange office near the train/bus station. (Exchanges in the shopping mall near the train station gives good rates though!)
If you exchange money you will end up with lots of 100zł (or even 200zł) notes. Try and use these as quick as possible, as you will need smaller notes/change when buying smaller items. You will have a lot of problems if you try and buy a 5zł magnet with a 100zł note! The city as a whole loves to use exact change when buying things, and you can get refused service if you try and buy something like a bottle of milk and you only have a 100zł (or even a 50zł!) note!
Also, when at a restaurant do not say thank you when they collect the money. They will keep the change as a tip. This has happened even if the bill is around 70zł and you pay with a 100zł note. (If you tip, 10% is normal, so even when it is obvious that the 'tip' would be too large, they will assume a "thank you" means keep the change!)
Read our famous and comprehensive guide to everything you need to know before vistiing Kraków!