Op-shop rubbish fees are piling up as people dump masses of 'unusable' items outside. 

The SPCA says it's spent $250,000 this year. 

Retail general manager Cathy Crichton says the charity's grateful to receive donations of quality items - but people also leave damaged or unhygienic items it must throw away. 

She says binning large items like mattresses can cost a lot.

"That, in itself, is eroding the good work that our volunteers and team members are doing and building fundraising - and that's the commercial challenge."

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