Charity shops in Beaconsfield are losing out on money and donations because items left outside are being stolen or damaged.
The problem is getting worse shops warned - with reports of thieves turning up in a van to loot goods from the street.
Lynda Harker, manager of Help the Aged, Station Road, said: "People are rooting through bags left outside the shop, usually over the weekend. Other customers have been seeing it happen."
She said the shops have encouraged people to leave their donations during opening hours.
But many items including clothes and books are still being dropped off in the evening or at weekends.
Despite being open seven days a week donations are still being left outside of opening hours, said Anne Coogan, manager of Cancer Research UK, also in Station Road.
She said: "Many items are donated through the evening and staff have found people stealing."
Jenny Develin, manager, Shaw Trust, Maxwell Road, said: " It's been going on as long as I've known - I've been here for ten years - but in the last year it's worse than ever."
"The other day when I came past the shop there were 10 bags, I thought I would put them in the shop when I came back, but when I got back there were none."
She said that customers had reported seeing people in vans driving up to the shop and taking bags.
"I think they're appalling. There's no words to describe them."
Oxfam,Station Rd and Iain Rennie Hospice at Home, the Arcade, Maxwell Rd said they had also experienced similar problems.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article