You haven't really described your precise application. Are you talking about a large amount of liquid in a bag -- say 5 lb (10 kg) of product in a single bag? Or are you thinking about just a small pouch of liquid like a wrapped stick of chewing gum -- more like CBChef's experience?
A bad reputation is quick to get -- it only takes one burst bag and one unhappy customer willing to complain to all.
If you're thinking about small lightweight pouches, I would store your product in-house for a time and see how it changes (or doesn't) with time. I would also package the product in the same bags and ship them to several testers to see how the bags survive the trip. Ship by every method you expect to use. I don't know what country you live in -- I'm in the US and in my experience, USPS mail usually handles small packages well, UPS is often rather rough, and FedEx also usually does well.
Moving on to shipping large amounts of liquid in a bag, I'm rather skeptical. Yes, the bags themselves are pretty resistant to bursting, but the heat sealed edges are not as tough and will split open from impact or being crushed. There is a lot of momentum generated when a 5 lb bag of oil is dropped 3 feet, and the seals must be able to withstand that kind of repeated shock during transit.
I use 5 mil vac bags all the time for freezing and short-term fresh storage of liquidy things (soup, stock, etc). Even though I love my vacuum sealer, I'm not too sure I'd ship heavy liquids in a bag as you propose. I would want to be able to heat seal the product similar to the wide seals made by the original manufacturer AND I would want to package the bag in a heavy-duty, super rigid box, kinda like the boxes that inexpensive "bagged" wine come in, to act as an exoskeleton for the bag. And if you do all that, you are pretty much back where you started with -- might as well use a bottle.
