My parents just left after a two week visit here in Peru. We had an amazing time around Cusco and the Sacred Valley, going to the jungle, and hiking the Inca trail to Macchu Picchu. While they were here I found myself explaining a variety of Peruvian customs Nansen and I have picked up over the last 7 months. Here is a list of examples:
Bargain on everything. This includes taxi rides, market purchases, and even while shopping in nice tourist shops. If you're buying more than one thing from the same person this is license to bargain even harder.
If you are in a nice store with actual price tags, offering to pay in cash (in effectivo) should drop the price 10%. This is before bargaining begins. If a store doesn't offer 10% for paying in cash they are playing hardball and/or trying to rip you off. This is an indication to consider going elsewhere.
If a Peruvian refuses to bargain with you it is for one of two reasons. One, they are actually offering you a fair price and you should quit bartering. Or two, they are being a jerk and you should walk away. It can sometimes be hard to know which situation it is, but trust your gut.
Things near the plaza and tourist attractions cost more. Inflation by location.
Peruvians hate making change. Always pay in exact if possible, or with the smallest bill possible. Give cents if you have it cause they hate breaking a sole too. This is becomes a problem because at some point you run out of coins and small bills. This is why its important to break big bills at shops and bigger restaurants whenever possible.
It is totally normal to be served a dish that includes rice, boiled potatoes, and french fries. Peruvians love their starches. The corollary of this is that is makes finding a vegetable difficult.
Peruvian food is pretty bland in general. Even if you can't stand spicy food you're probably safe having a stuffed pepper.
Local restaurants use this green sauce. If its too local of a place the green sauce can sit out for days and get you sick. Best to only eat it if there are a significant number of other tourists in the restaurant.
If there are 50% or more tourists in a restaurant it is safe to eat anything, including raw green leafy vegetables.
Produce and fruits and really cheap. Meat is more expensive. Being able to go veggie for a while has the potential to save you a lot of money.
It is impossible to find really good cheese besides Andean cheese. Quit trying.
There is a huge variation in mark-up on imported American products (think granola bars, pancake mix, macaroni and cheese, pringles, etc). Shopping around for prices is important.
The one exception to this is M&Ms which are always the ridiculous price of s/3.50 (about a $1.50) a pack everywhere except Gato's, where they are s/3.00.
Baked rolls are ridiculously cheap at s/0.20 each.
Generally the more uncomfortable something is, the less expensive it will be. For example combvi's that cram 25 people in a space designed to seat 10 are cheaper than big buses with individual seats are cheaper than any form of transportation with the word "tourist" on it. Buses with bathrooms are the most expensive of all but totally worth it for long trips cause Peruvians have bladders of steel.
Some drivers will drive crazy fast to get there asap. Sometimes this is good, sometimes it makes you fear for your life.
Bus tickets do not need to be booked in advance for typical buses. 30 minutes in advance is often enough. This is not always true of really long buses and never true of buses catering exclusively towards tourists.
Cruz del Sur is almost always a rip. Although they do serve you tea which is nice.
Private tourist drivers are always the best and the safest. This is a fact, not an opinion.
Buses around Cusco have definite routes, but no map posted anywhere. There are also no scheduled times, the bus gets there when it gets there. All bus rides are s/0.70.
You don't tip taxis drivers.
Peruvians operate on Peruvian time, which after careful observation can be up to 2 hours later than the originally stated time. Only later, never earlier.
This is true of appointments with very specific times as well. These are more like suggestions than actual committed meetings.
Peruvians have a vague sense of days as well. "Come back Friday" can actually mean as late as several weeks later.
Always bring a book if you're meeting a Peruvian. It makes waiting much less infuriating.
The only time Peruvian time does not apply is with any kind of tour operator. In this case, things will run like clockwork and you better be on time. Real time.