My advice and this has worked for me very well:-

1) Don't pay in cash for large purchases!
2) Pay only a booking deposit!
3) Don't pay full amount for delivery months ahead!
4) If have to pay the full amount, delivery must be within 1-2 weeks time!
5) Get everything in writing including promises and freebies etc!
6) Take pictures lots of pictures, of items purchased!

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1) If paid with CC esp with Citibank raise a payment dispute and halt payment to the vendor.
2) Where possible deposit a small amount and not risk the entire amount.
3) When it comes to raising a dispute the sooner it's reported the better. Old cases are hard to trace for everyone including buyers, vendors and payment companies!
4) The faster vendors deliver the better, only a small window for buyers to raise a payment dispute with CC companies. Make sure the delivery date is written, black and white on invoice!
5) Documented proof is important, helps builds a case against vendor etc.
6) Picture says a thousand words and it's documented proof if product delivered is significantly different from purchases.