Postage higher than expected

[dtnefish_1]

I have sold an item but wrongly estimated postage costs at £20. The buyer has paid his deposit pending delivery, but I now discover postage will be £50. Can the buyer increase his deposit to cover the extra £30 before I send it off? There will be no incentive for him to pay once hes got the item (except a bad review from me!)  

[john1297576]

As deposits are not allowed, then answer can only be NO.

As you cannot leave anything but positive feedback, that is an empty threat, as negative comments on positive feedback can be if reported to ebay, and you would no doubt get a defect or warning.

On ebay buyer pays in full.

[plpmr]

"The buyer has paid his deposit pending delivery,"

Exactly what does this mean?

Taking payment outside eBay is not allowed [deposits] and you cannot put your phone number in a listing asking buyers to contact you.