I occasionally sell items via Kijiji and Craigslist in Canada, and while cash is convenient sometimes it's easier to do electronic transfers, or even have the ability to accept credit card in person. I have found Paypal and Square offer easy to use system for accepting payments electronically. They both allow credit card use.
Square prices are hard to beat for a small operation. I've looked around when I was considering starting up a business, and they're definitely one of the cheapest. Paypal are the second best, but I do not trust Paypal in general.
However, looking locally may provide you some more options. If you walk in to one of the local banks, you may be able to get offers for merchant accounts with better rate, depending on your relationships with that bank.
You can also check out Costco merchant services, they seem to be quite competitive with the rates, but there may be other costs (they will probably charge more for equipment).
Canadians can email or text each other money through Interac. It is fast - the longest it's ever taken for me is 20 minutes, often it's less - and secure. You don't need to know each other's banking details or even real names. I've used this to send money to my children, each of whom uses a different bank than I do, and they've used it to send money to friends to pay for concert tickets and the like. You add a security question so if someone else got to the email or text first, they wouldn't get the money. I also get an email once the transfer has gone through, so I know they got it.
Some banks limit this to $1000 a day, mine to $3000. Typically there is no fee for the recipient and $1 or $2 for the sender. A dollar on $1000 is way better than a 2 or 3% cc processing fee. But even for $30, a dollar is like 3% and you didn't need to apply for anything or set anything up, and your customers don't need a credit card or to trust you with their credit card details.
I keep meeting people who don't know about this. Everyone with a Canadian bank account and an email address or smartphone should know about it.
For people who frequently submit payments via PayPal, you may want to try and negotiate with them to use Paypal mass payments. Although the mass payment program is designed to send small amounts to many people, you can process payment batches of 1 transaction.
In the CA mass payment fees (paid by sender) are 2% capped at 1.25 CAD To CA and US. International payments are 2% capped at 24.00 CAD. No fees for receiver. A business PayPal account is required to enable mass payments.
When I mention this to customers, many are unaware Paypal's mass payment program exists!
I know this won't be a popular answer, but here goes: Bitcoin.
Regardless of how you feel about the long term prospects of bitcoin, it actually works very well as a way to transfer money with hardly any fee. You can go online, buy bitcoin, transfer them for a very tiny fee, then the person on the other end can cash out in their own local currency.
In fact, bitcoin is gaining a lot of popularity in some countries for this very reason. It is becoming more common for one family member to come to America or Eurpoe to work, then use bitcoin to transfer money to their family back home. This works so well because even international transfers have such low fees.
The best place to get bitcoins will vary depending on where you live. I'm American, so I use Coinbase. I believe Bitstamp is popular in Europe. I'm not sure about other countries.