New investor questions - 14 unit apartment building

Hi BP! I am a new investor and have been looking for a single family or small multi-family property for my first deal. While looking, I actually came across a 14-unit apartment complex in my area that looks (at least to me) like a great deal.  Below are the concerns I have regarding the property.

After looking at the tax records, the property has been sold 5 times in the last 15 years (red flag?). Secondly, each time it has been sold for around $230,000; however the seller is asking $375,000 for it (and from a drive-by I can tell he has not put $145,000 into it). What could explain this large difference in price? There are currently 3 vacant units, so how would that affect the purchase price?

Thanks!