DPF Question

Hi, new to this forum so hello all. I am after some advice regarding the dreaded DPF. I recently purchased a BMW from a garage which has been fine. However, I recently encountered a problem and I have a fault code reader device that can also read engine parameters etc. Whilst doing the checks I also checked the dpf back pressure and it gave a reading of zero millibar. Mmmmm, the car doesn't chuck plumes of black smoke out but I do notice the odd puff of soot if I put my foot down. There is also a little bit of soot around the tail pipes. Anyhow, I did some digging and found a phone number on a receipt so gave it a call and got hold of the previous owner. He confirmed that the dpf has been gutted and the car has had a mild remap. I have now spoken to 3 MOT centres about where I stand, one of them lifted the car on the ramp and basically said he could see no evidence the dpf had been tampered with so don't worry about it because it will pass. Now, I'm still a bit uncomfortable because, technically, the car is not road legal. The thing is, I rang BMW and a new dpf is, ahem, £2070 for the part alone. I absolutely love the car but do I demand that the garage pay for the dpf reinstating? I have a feeling they will decline so do I ask for my money back? There are one or two rumours on the net that another test will be introduced to counteract the practice of gutting the dpf. Has anyone heard this? Would just like to hear people's opinions on what to do because there are so many mixed opinions, it's just a big grey area. Any help much appreciated. Andy