Poor sealing or poor vacuum?
I am getting close to end-of-life on my second FoodSaver, but I use it. A lot. I cannot question that I got my money's worth. But at the moment, the gasket material is a bit dried out, so it gets stubborn about sealing.
I run a line of olive oil over the gasket when it gives me troubles, problem pushed back another two months.
Bad seals on mine (from inadequate heating) tend to be either wrinkled bags, or too much liquid getting sucked up as far as the seal (rare, but it happens.) I've taken to doing the following, especially for sous vide: 1) Put the food in the bag, set up to seal normally. 2) Hit the go button, let it pump and seal as normal. 3) When it stops, _quickly_ unlatch and latch the latch. Now press "Seal." You get a second seal in the same spot, sometimes the little extra bit of heat fixes the problem. For SV I will then pull the bag back a quarter inch and seal again, just to be sure.
Of course, if you're doing 20 bags, this is a pain because the sealer overheats and locks you out. But I'm rarely doing that many at once.
Other than that I really have no advice, I'm on about year 6-7 on this one and it is still running.