'88 wasn't the best year for Ford 4x4 trucks, but a Bronco is still a good vehicle and you'll certainly enjoy owning one.
The '87-88 front locking hubs are known to be a weak design; so much so that Ford went back to the '86 style in the middle of the '88 production year. If the hubs on this truck are held on by the lug nuts, it's not as desirable.
Also, they used 2 fuel pumps from '87-90 and this system is also prone to problems.
The '87-91 ignition system uses a module bolted directly to the distributor, and Ford is being sued right now for continuing to use this (TFI - thick-film ignition) even after they knew it was prone to failure.
However, knowledge is power and since you know what systems are going to give you problems, you can fix them before the truck breaks down. But they also give you some good points to argue to get a lower price. If you like the truck, buy it, but know what you're buying. Things I'd check are:
How many times has the odometer rolled over?
How much tread is left on the tires?
Do the brakes need to be changed?
Was the truck used for towing?
Was it wrecked?
What has been repaired or replaced?
Who performed the maintenance & repairs?
Was the automatic transmission fluid changed regularly?
Are there any fluid leaks?
Does the seller know of any problems or repairs that are needed?
How hard will it be for you to get replacement parts for it?
If you can't do the repairs yourself, are the local repair shops familiar with this vehicle?