I am not an expert in this area but I will share some of the things I found out as I did some research for my own company.
There are many different companies and banks that can fill the need but I can not stress how important it is to do your research. When I first decided to do shows last year I Googled "merchant services" and I was given a number of options to choose from. I did my online research but there were many questions with the big one being about costs. Although very quick and easy to have a card reader especially a wireless one, it can add up to more than you are willing to spend.Some of the charges that can add up are:
1.) monthly service fees
2.) monthly wireless connections fee (just like a wireless phone fee)
3.) credit card processing fees, these vary between types of cards and sometimes depends on the amount being charged.
4.) statement fees (there is a charge for the company to provide you with a monthly statement of all transactions)
5.) equipment rental or purchase fees and a wireless card reader can run up into the hundreds of dollars.
Just be sure what you are getting and what it will cost before you sign any type of a contract. Some companies will offer a "no contract" setup but often these require that you process a minumum amount of transactions per month. When I was contacted by one company I was told that I could get a refurbished card reader and I later found out that these so called refurbished card readers would be obsolete within 4 months because of new laws concerning the type of printouts they were using. I found this out after researching the equipment model and cross referencing with a number of other companies. Just as with any purchase be sure of what you are getting and what it will cost you in the end.
The next two options can be accessed online through a wireless connection. You can check with the show organizers if there is wireless services available, sometimes it is free and sometimes there is a small charge. You could also use your own wireless connection card for your computer, if you own one or an iphone.
Just by chance a show organizer was the one that told me about "Propay", http://epay.propay.com/, an online service with fees that start at $34.95 per year and can be upgraded depending on the services required and of course, the fees increase with the amount of services. I found it very easy to sign up and was ready to go by the next day.
With this service you can process cards online with the ease of a card swiper(card reader is an extra charge) that attaches to your computer or you can store info on the card swiper and download it at the end of the day. If you do not have a laptop you can use your iphone or process individual purchases by phone very easily. My one bit of advice if you plan to process by cell phone is that when you sign up use your wireless number as your business phone. When processing transactions use the cell phone that is listed as your business phone on your account, this will make it easier and cut down the number of steps required. Your funds are processed within 1-3 days and can be transferred to you bank account or you can get a prepaid mastercard to use your funds directly through Propay.
There is also another online system called "Intuit" http://www.intuit.com/ that can be used with Quick Books and although I have not reasearched all its aspects it does sound very reasonably priced at $12.95 per month. This is a good price for someone that is just starting out and there are no contracts to sign, so cancellation can be done at any time. This service can also be used to process cards on sight with the use of a laptop and a wireless connection or you can use your iphone. With Intuit your funds are deposited directly into a business bank account within 1-3 days of when transactions are processed.
Both of these last two options are user friendly and you can access your statements online and print them out at home if you like. I do suggest that if you choose to do Propay or Intuit you do the online sign up at least a week ahead of time just in case you run into any problems.
Remember you are not required to take credit cards at all and sometimes show organizers will provide a check cashing, credit card station for a small fee that is either paid by the vendor or the customer. Another idea is to check and see if there is an ATM available where customers can use their debit or credit cards to access funds. Some vendors will set a minimum charge that they will process, be forewarned, this is against credit card rules of use. According to Mastercard Company, it is considered discrimination to only allow charges of a certain amount or to charge a processing fee. You can read the rules of use for Mastercard at http://www.mastercard.com/us/merchant/support/rules.html
Visa rules of use can be found at http://usa.visa.com/merchants/index.html#/page2
I do hope this information is helpful and I do not claim to be an expert in this area, so please do your own research before you decide which type of credit card merchant account to use, if you decide to accept credit cards.
As always remember to have fun and smile.