Paying your loans on time is a great way to improve your current score.  

Another thing is, in January, when my tenants leave, I'm going to do a little improving on the house and I can probably go from 5520€ to 6720€ (net profit per year) by bumping up the rent 100 €/month.From the credit simulations I've done the mortgage will not cost that much.

People rarely actually care about what you really need and are more interested in commission, pay, etc.Wish there was a way to improve the industry image, but it seems that there is a correlation to your level of shadiness and your success. 

Any improvements put into the house for the flip get added to what you paid. 100k purchase price50k improvements150k basisSell for 225= 225- 150= 75000 gain taxed at whatever capital gains rate applies to your normal tax rate.

Before I joined the Army I did home improvement side jobs, i.e. paint, dry wall, tile, carpeting, roofing, little bit of framing, pressure washing, junk removal, lawn care.

She did a quick title search on the deal and found that the guy who bought it purchased the property under an LLC that is in arrears to the state-- she says that it will be nigh impossible to get clean title to the property in this case, and to even sell it looks like his LLC needs to pay near $10k in back taxes and filing fees--I know they guy doesn't have that money, and I'm not in the mood to pay him that extra dough just to get his books straight. 

Try not to over improve the condition of the property, as college kids will be kids and undoubtedly through the occasional party, and generally have less respect for property (I did).

I attempted to refi out my improvements but this failed.

But don't forget all your other expenses - taxes, insurance, utilities, landscaping, municipal rental license, HOA fees, reserve for repairs/improvements. 

Now, if you have a commercial tenant they have lease-hold improvements they can account for such matters, but not residential tenants.