Chanlo,
I have been in the IT industry for over 14yrs and whilst I am not a PHP coder myself, I have plenty of clients that do have their web stores linked to their SQL back-ends.
You say you have done a little HTTP and some CSS, so you sound somewhat unqualified to make such a statement. Happy to be corrected though...
You do not need to be a PHP 'genius' - you just need to be an experienced website/web store developer that has linked web sites to databases. That is like saying to need to be a genius to strip and rebuild an engine from the ground up - you don't need to be, you just need to be experienced in doing that process, which a trained and experienced mechanic could do with their eyes closed.
I spend most of my time setting up hosted infrastructure in BIG data centres (like entire multi-story buildings) and migrating clients from having physical servers/PC's on their premises to having virtual servers/PC's hosted in data centres (cloud hosting) on shared infrastructure - that is, instead of one server running on each physical server, we have dozens of virtual servers/PC's running on each physical server. Some people would say you need to be a 'genius' to do that, but you don't - that is just my skill set and for me it is a case of "Same s*#^, different day - just the client names, domains and IP subnets change.
It is not rocket science or ground-breaking tech to link a web site/web store to a database. It has been done by countless business for the last 5-10 years.
As an example, plenty of small computer components resellers such as UMart, MSY, PC Go Go, etc (who are not clients BTW) have had their web stores linked to their DB's for years.
There is no shortage of web designers that could do this for them and the cost would be in the $5-15K region to set up. Like I said, an insignificant cost for a business of their turnover and the cost is a tax write-off. There are also plenty of off-the-shelf products that do it, but some customization is always required.
In terms of the 'model' for how they do it, they can either run one DB and have the both the bricks-and-mortar shop and web store point to that OR run an in-store DB and a hosted DB for the web store and have the two databases sync to each other. The latter options is preferable from a redundancy POV.
Maybe they should talk to Di from LFI - she runs a web design company and she seems like a reputable person to deal with.
You can stop making excuses on their behalf now.
Ben.