Please. Don't try to exaggerate that one or two incidents and make it sound like buying invoice is very risky.
I just started collecting HT last year and I have bought over 10 invoices and never had a problem. Just buy from the ones with good rating and check toys daily or HT Facebook regularly and you will know when the figures are ready to pick up.
If you did not preorder in time and you really want the figure, buy invoice early instead of wait till the figure comes out and then buy invoice should be the most economical way already.