I'm surprised that the OP has not given us the most important and basic fact about these units, i.e., what is the expected yield from them expressed as a % of the selling price. Taking this thought process further, why on earth would a developer be letting valuable commercial in the city centre off to market without either considering holding it himself and leasing it out, or why is it not being sold with the benefit of a tenant?
Empty shell and core commercial in a city centre may well be valuable (depending on exactly where it is), but if it is being sold like this with a "discount" then it is being aimed at amateurs, and has probably already been looked over by the serious players and found wanting. In the unlikely event that the experts have just simply missed out on this "opportunity" then the correct approach is to see what similar sized units in the area are yielding, and apply that factor to these to get an idea of potential value. Factor in a year without tenants into your business plan -- the % yield can only be truly measured for tenanted property and you would need to be getting this one at a lower price.
If of course you buy the unit and then install a quality tenant giving a yield in the high single digits, you have probably created a product that can easily be resold at a profit. On the other hand, trying to flip an empty commercial property is pretty much imposible, unless you meet another gullible paddy!
The approach being made by the OP to the issue of commercial property shows a complete lack of knowledge of the realities of the market, and in this instance I would advise him to go back to first principles and make a cold evaluation of the value of the investment. If it still looks good, then go for it, but ignore the notion of a "discount" -- doesn't work like this in real life.