Should V brakes be able to lock the front wheel? I recently bought a folding electric bike for commuting by train, and braking has been a constant pain.

The shop has adjusted them most weeks, I've never had a bike need this much adjusting, but they won't even entertain the idea that they could be faulty.

Today, they've changed the brake pads, after less than 200 miles use, and when I've come test the bike, the front wheel doesn't come close to locking (nor does the rear of the bike raise off the ground), and the bike will casually come to a stop.

The mechanic has just argued that v brakes function like this and should not lock the front wheel, and he couldn't make them any more effective than they are, I explained that every bike I've ever owned with v brakes was able to lock the front wheel, but it just felt we weren't going to see eye to eye.

So, should v brakes be able to lock the front wheel?

Update
To clarify, the bike has at times been able to stop much more sharply than it currently is, on delivery, the brakes were okay, and after each previous 'adjustment', so the weight is not the problem. It can 'endo', the claim by the mechanic is that it shouldn't be able to, and that configuring the brakes like this is fine.

A few details, which were requested in the comments:
It has 20" wheels and weighs 18kg,

Here's a picture of it:
Regarding locking the front wheel, they are sort of correct: on paved surfaces and tires with decent grip the rear wheel should lift off the ground before front wheel locks. 

However, it sounds like you can't lift the rear wheel either. A decent set of brake pads should last much longer than 200 miles and brakes should not be adjusted every week (unless you ride 2000 miles in a week), so it's probably best to switch to a different shop. It might also be that the brakes are just garbage and could be replaced with a better set. As mentioned in a comment, a brake booster arch might also help.