Hello BP family, a question for you all.

So I recently visited one of the fourplexes in the state of FL and want to use the BRRRR for the first time.

The property is selling for 170k- need about 20k rehab and according to the realtor the ARV is 240k.

He said the number is base on the similar house that was sold around the area,   

but my question,  how reliable is this number?   Can I pay appraiser beforehand to see what they think it will be worth it?

Any recommendation or tips to confirm the After repair value will much appreciate it 

Thank you all