The treats aren't the problem and there is no reason to change methods or use treats sparingly. IME using treats to train is extremely effective,easy and builds a great relationship between dog and handler.
That said, your wife's technique could improve. She needs to use a variable reinforcement schedule once the dog will willingly offer the behavior. When in the teaching phase of training you want the rate of reinforcement very high, a treat or reward for a behavior. Once the dog willingly offers the behavior on cue every time, the reinforcement schedule should become more random. If it doesn't, it creates a lot of frustration in the dog. The difference is like a soda machine and a slot machine. If you put money into a soda machine, you expect a product in return. If you don't get the product, you get frustrated and generally give up on putting money in that machine pretty quickly. However, no one puts money in a slot machine expecting something in return every time. People put money in a slot machine because of the chance of a reward - variable reinforcement schedule. Right now it sounds like Max is expecting a treat for every behavior. For the ones he is really good at, strat having him do "Two-fers" and "Three-fers". Have Max sit two times before getting a treat, three times before getting a treat, one time before getting a treat, three times before getting a treat, etc.
Three hundred peck is another good method for teaching dogs to go longer without a reward and is an excellent way to build reliability and add a variable reinforcement schedule. Three hundred peck is named after a behavioral experiment where a pigeon was trained to peck a bar 300 times before getting a reward. Start with having Max sit one time before he gets the reward, two times before he gets the reward, three times before he gets the reward, four times before he gets the reward, ect. Once you get to the point where he is hesitating to sit on your first cue, go back to one sit for the reward and build your way back up. Once you have him reliably sitting 10x for the reward, ten can become your base instead of one most of the time. Then fifteen cam become the base, then 20, etc, etc. But only up the base when he is easily and always getting to at least 10 and even then, occasionally go back to one. This method is extremely good for teaching stays, simply add one second each try. Dog sits for count of one, reward. Dog sit for count of two, reward, Dog sits for count of three, reward. Dog sits for count of four, reward. Dog doesn't make it to count of five? Back to a count of one for the reward. The counting should be done in your head/silently
I would also suggest the use of a behavior marker, to tell Max what he did to earn the reward. A word such as "yes" used as the behavior happens/before the will tell Max that a treat is coming and why. For example, if you are teaching sit, lure the dog into position using a treat and as his butt hits the ground, say "yes" then give the treat. The treat always comes after the marker word. The marker word is only used when it will be followed by a reward. This will help lower Max's frustration, as it will make the training much more clear to him.
Another great exercise for food obsessed dogs is teaching what many people refer to as "Doggy Zen". I call it "Off", people commonly call it "Leave it". But this is not leave it done in the traditional style (put a treat down and correct the dog for trying to get it). For this, your dog will be trained to first back away from food in your closed hand, then in your open hand, then in other places (chair/floor/etc). It is self control on the dog's part, not forced control by the owner. Show your dog a treat in your hand, close your hand and just wait for him to back off. The first few tries, very food driven dogs will seem like they will never stop trying to get the treat but just wait them out. As soon as the dog backs off, even just for a second say "yes" and drop the treat. After the first few tries, even the most food obsessed dog learns that he can't forcefully get the treat. Once the dog starts offering to back away from your hand, you can start saying "Off" (whatever cue you'll use) but say it just one time. Once your dog backs away from your closed hand when you say off each and every time, start doing 300 peck. Off for a count of 1, "yes"/treat. Off for a count of 2, "yes"/treat. Off for a count of 3, "yes"/treat, etc until your dog doesn't stay off for the full count, then back to one. Only move to an open hand when your dog will solidly leave the treat in your closed hand for a 10-20 count. Once you move the the open hand, start totally from scratch again, rewarding for the dog backing off at all then starting 300 peck. Only when your dog is solid on closed and open hand will you move to attempting it on a chair and/or floor.
