Every time I have ordered they correct the price at shipping and I don't have to contact them
You must have had the odd occasion as lot of members here will tell you they get charged the price they ordered at and was not reduced if price dropped before release date with lot of previous zavvi orders.
This is why most reorder at cheaper price and cancel their original order as it's not worth the hassle contacting Zavvi to get refund of price difference.
Zavvi have on a few occasions reduced the price on orders when taking payment but most times they don't especially if you live outside the UK and if price drops due to currency exchange rate been different but UK sterling price not changed.
Zavvi also wont give pre order price promise if a discount code was used on a order as per zavvi pre order price promise terms and conditions.
Zavvi did do it for everyone for the fright night steelbook the cheaper price for those that ordered at higher price and kept that order they gave refunds a few days after the difference in price most here was not expecting that to happen.
This release though is £24.99 Zavvi told me in a twitter private message the £22.99 price showing on the website before it went live was a price error and was meant to be £24.99
I don't think they knew for sure the price and was a mistake telling customers a few days before it went live that it would be £22.99
Edit
Wednesday 15th Feb
Zavvi have reduced the price to £22.99
They did say in the twitter message
We’ll check with the team to see if this is the correct pricing