2 types of paying by card. One is to authorise it in front of customer. That's the expensive method.
(2 lots of monthly fees as well. Terminal rental and minimum charge for processing transactions.)
Secondly you take their card details and process the transaction when you get back home. The terminal is a lot cheaper but the transaction costs are higher as this is deemed a "card holder not present" transaction" and which are always considered more risky.
Paypal also has it's limitations although I can't remember exactly what they were since I looked into it a few months ago. I think from memory to have a half-decent pay pal account for what you want (eg needs to be in your business name to continue with the idea of looking professional) the costs start to come out about the same as going down on of the major providers of these machines. You also still have the problem of people wondering if you are harvesting their personal information as you will still need to take their info away to process or worse still wait for them to remember to pay you. (And I bet we would all wait for all our wonderful clients to simply pay us!)
Benefits of paying by card are that custy MAY spend more with you, and also the funds are guaranteed (no bouncing cheques).
Funds are also electronically credited to your account so in many cases will lower bank charges. they also appear as cleared funds so can be used straight away. If you get everybody to pay you that way it'll also save on having to make a special trip to the bank and possibly queue up inside, so it's more time efficient.
There are a few other "hidden" costs to also consider like disputed transactions/charge-backs etc. There is usually also a minimum charge based on the level of activity on the machine.
If you went for the second, cheaper option your customer may not be happy about you walking away with their card details although that is in effect little difference to you capturing the info when authorising it in front of them or indeed taking their bank details off their cheque.
Paranoia rules ssh I'm not telling you