A scam which transcends nationalities, this actually happened to my cousin in Manchester
When visiting temples, helpful people will offer you incense (for praying), you assume it's free or at a lowish price, take it, burn it, then they charge you ridiculous amounts for it. This is primarily aimed at Chinese people though, as TCG will laugh in their face and tell them to fuck off, while other people who are not shameless will hand over the hugely inflated fee.
Temples in HK don't do this, as you have sellers right there and then to sell you them.
Temples in the UK DO DO THIS TOO.
Either buy your own or go to a vendor cart nearby where you see other people buying such things.