If your planning to accept cards through the website then your site must be 128 bit secure, required by all banks and card merchants.
There are other payment methods where you don't need this, but when your customer gets to your payment page they will be transferred away from your site to the merchants site. Personally I hate this.
If you're accepting cards onsite you need more than just an SSL certificate, you need an underlying professional, robust, secure system, and you might need a system that ticks other boxes like
PCI compliance.
An SSL certificate alone doesn't mean much, and it certainly doesn't mean that your credit card details are safe with the company behind the SSL website.
It is pretty easy for a website to set up an SSL certificate and then ask for credit card details, there doesn't even have to be an automated e-commerce system behind it.
The SSL only means that the connection and the credit card details are secure as they pass from the user's web browser to the website with the SSL certificate (that is if the web page's form actually HTTPS posts the details back to the secure site, which isn't always the case in very badly designed sites, but someone in the know would be able to notice this, unfortunately the general public might not).
Once the credit card details arrive at the SSL website the owner can pretty much do what they want with those details in any insecure way they please. This is why the general public should only send their credit card details to sites and companies they have heard of and trust.
Personally, I wouldn't submit my credit card details directly to a small online shop that I'd never heard of before even if it did have an SSL certificate. You don't know who you are dealing with, you dont know whether the underlying systems are secure or even automated, you don't know the integrity of the people behind the shop, you don't even know whether its a bona fide shop or just a con to get your credit card details.
This is where the third party off-site trusted payment provider site/company comes in, a site/company which you have heard of and one that you trust, like PayPal or WorldPay. And that is why, in my opinion, small shops shouldn't even be thinking of taking credit card details onsite.
Put yourself in the position of the customer. If they have got to your site from the search engines then they may have never heard of you before, in which case they should prefer to divulge their credit card details to a site they have heard of like PayPal or WorldPay. It's a matter of trust. Just because big sites like Amazon take credit card details directly on their site, it doesn't necessarily follow that a small company's website selling to strangers should do so too. If you haven't got a well-known or trusted brand, then you are better off relying on a payment site that does.
As for sticking so-called trusted logos on your site, that is meaningless to the informed surfer. Anyone can put a logo on a website, in fact that's exactly what phishers do to pretend their site is the real thing.
If you are taking credit card details onsite, it also doesn't help with trust if you have anything on your site that indicates that the site isn't professional, like bad thumbnails or very slow loading pages (associated with either cheap hosting or bad design/programming). Informed customers will think, if they can't get simple things like that right how good is their underlying security going to be?