B- How validate compliance with PCI DSS?

No. SSL certificates do not secure a Web server from malicious attacks or intrusions. High assurance SSL certificates provide the first tier of customer security and reassurance such as the below, but there are other steps to achieve PCI Compliance. See Question “What does a small-to-medium sized business (Level 4 merchant) have to do in order to satisfy the PCI requirements?”
  • A secure connection between the customer's browser and the web server
  • Validation that the Website operators are a legitimate, legally accountable organization
The payment brands may, at their discretion, fine an acquiring bank $5,000 to $100,000 per month for PCI compliance violations. The banks will most likely pass this fine on downstream till it eventually hits the merchant. Furthermore, the bank will also most likely either terminate your relationship or increase transaction fees. Penalties are not openly discussed nor widely publicized, but they can catastrophic to a small business.

It is important to be familiar with your merchant account agreement, which should outline your exposure.
Cardholder data is any personally identifiable data associated with a cardholder. This could be an account number, expiration date, name, address, social security number, etc. All personally identifiable information associated with the cardholder that is stored, processed, or transmitted is also considered cardholder data.
For the purposes of the PCI DSS, a merchant is defined as any entity that accepts payment cards bearing the logos of any of the five members of PCI SSC (American Express, Discover, JCB, MasterCard or Visa) as payment for goods and/or services. Note that a merchant that accepts payment cards as payment for goods and/or services can also be a service provider, if the services sold result in storing, processing, or transmitting cardholder data on behalf of other merchants or service providers. For example, an ISP is a merchant that accepts payment cards for monthly billing, but also is a service provider if it hosts merchants as customers
Any company that stores, processes, or transmits cardholder data on behalf of another entity is defined to be a Service Provider by the Payment Card Industry (PCI) guidelines.
What constitutes a payment application as it relates to PCI Compliance? The term payment application has a very broad meaning in PCI. A payment application is anything that stores, processes, or transmits card data electronically.

This means that anything from a Point of Sale System (e.g., Verifone swipe terminals, ALOHA terminals, etc.) in a restaurant to a Website e-commerce shopping cart (e.g., CreLoaded, osCommerce, etc) are all classified as payment applications. Therefore any piece of software that has been designed to touch credit card data is considered a payment application.
Payment Gateways connect a merchant to the bank or processor that is acting as the front-end connection to the Card Brands. They are called gateways because they take many inputs from a variety of different applications and route those inputs to the appropriate bank or processor. Gateways communicate with the bank or processor using dial-up connections, Web-based connections or privately held leased lines.
Source : GIE-CB