Simply, I would reduce my offer equal to the amount of the repair cost below what I would pay if there was no need to do the repair.
If you know the perimeter of the house in feet, devide that number by 6 or 7 and that will tell you how many pressed piles you need. Pressed piles cost about 200-300 each depending on how deep they need to go (total foundtion repair likely about $10,000 for a 1,200 SF structure). There are other better repair methods but they cost more (usually twice as much and up). If you are gonna flip it, you might not be concerned with the "lifetime warranty" of the repair, if offered, but if you are going to hold it for more than one season (wet season to dry season or vs/vs) you will want that lifetime warranty so you can call them back to shim up the foundation because it WILL move again.....and again and again -you get the point.
Some foundation movement is to be expected in many areas of the metroplex, but I would advise staying away from those houses that evidence a lot of movement. The movement never stops and it's a never ending sheet rock repair and door and window shimming story. Those neighbors slowly fixing their houses will likely never be done with it.
FWIW, I am a geotechncical engineer that invests part time in real-estate, so my input on the foundation proper is sound. But if you REALLY should or shouldn't invest, I am not the most qualified to say. If the movement looked bad to me, I wouldn't do it. But you may not know how severe the movement is unless you have experience evaluating such things and have a basis to compare.