HI,
If they have purchased from you before with no problems, then I wouldn't anticipate further issues. At least they have contacted you to let you know - which is more than some would do.
If a buyer has a card registered with PayPal it acts as 'backup funding' and makes payments through thier bank instant. If no card, then it will be an eCheque which will take up to 10 days to clear into your account.
Buyers have 4 days from listing end to pay for items before you can open a dispute and you can't close for a further 4 days. Some sellers open when time allows, others may wait a few extra days. I don't usually open until day 6/7 and if a buyer was to contact me to let me know of problems, I'd be happy to wait.
As long as you meet ALL the criteria for Seller Protection then you should be o.k.

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