Don't change any more money than you need to reach your hotel at the airport.
In April the fixed rate for the Euro was 1.95 leva=1 Euro.
At the airport they gave me only 1.65 leva to the Euro!
Also best to use banks only to exchange money. Bring your passport with.
Unique Suggestions: Change only enough at the airport to reach your hotel.
Fun Alternatives: Not too much alternative here. Just remember to wait until you can get to a bank to change more money.
Not strictly a trap, but some info to consider. The town has dozens of (house) museums. As for the museums some of them are a bit overrated and disappointing except when you are really into the subject it can excite you. The 3 museums mentioned on this page are worth visiting and prominent. As for house museums: remember that none of the displays are in any language but Bulgarian and that the staff rarely speaks English. Also, in case you are not into architecture that much, after 2 or 3 houses you might have had it, considering each house has to be paid for again.
There are tones of them in Plovdiv. They are so nice and vivid people but some of them are stealing so well.