Should I be concerned that my local big name filling station is using a local supplier for it s fuel?

It all comes from the same refinery. Unlike boxes of soap powder what it says on the outside isn't always what's on the inside. The fuel transporter is just using the wrong branded tank but it will have the correct fuel inside.

If you've been refuelling whilst the tanker has been making a delivery that may have stirred up some sediment from the bottom of the tank. Never fuel up when a delivery is being made.

possibly. but also: don't fuel up when the tanker is filling the gas station. it stirs up deposits that can get into your car which could lead to engine issues. wait maybe an hour after the tanker leaves so the deposits settle.

It's common practice. The sign on top of the filling station means nothing. They may have purchased gas from Shell, or other brand.

Nice try...now have someone that knows how to diagnose motor problems look at you vehicle. You'd be better off trying to explain what the problem is on this site.

That big tanker with their name on it gets the gas from the same place the other trucks do

Local suppliers are Supposed to provide exactly the same thing as the big-name suppliers.

The reality is that all fuel starts out basically the same.

What makes each brand different is the additives used,

which are commonly dumped into the tank on the trailer

for a specific station to which the fuel will be delivered.