Shopping in Cozumel
Lots of items for sale don't have price tags for a reason. You're supposed to haggle. It only takes a little bit of time and it's fun and it's expected in the owner-operated open air markets and beach/street vendors. If an item does have a price tag, go ahead and ask how much it sells for, they might tell you a lower price!
Silver jewelry and Tanzanite jewelry is sold in abundance here. When is comes to silver, be sure it has .925 stamped on the back for the highest quality.
Partying in Cozumel
There are street vendors down the main strip who will sell you drinks and street merchants who will give you free shots of Tequila. The loudest, funnest places to party in Cozumel is Senior Frog's and Carlos & Charlie's. Upon my visit, Carlos & Charlie's was a bit too loud and ruckus but I found the service, food and atmosphere top notch at Senior Frogs. Try a drink from "The Yard" plastic cup. It's a great souvenir.
Weather in Cozumel
As Adrian Cronauer says, "It's hot! Damn hot! Real hot!" Even in March, it's frickin' hot in Cozumel. According to weather.com, the average low is 68F December through March and the average high is 82F to 85F. Stay out of the sun and be careful with the liquor. Use your sunscreen.
The rainy season for the whole Yucatan peninsula is from October to January and April to July. That makes the best times to go from Feburary to March and August to September.