New Tax assessment on a cash sale?

[Josh W.]

I’m looking at a McKinney TX property that was built in 78 and sold for cash in 2018. The tax assessment is at 75k and did not reset when it was sold in 2018 for 200k. He put a lot of work into it, I am looking at purchasing for 300k. If I purchase cash he says the deed of record only says “purchased for 10$“ and it will not set off a flag for a reassessment.

Does anyone have experience here?  If I finance 150k and record the deed for a 150k sale, would it set up a reassessment?

I’m also looking to add a 150k garage/out building addition. Would financing this addition change the valuation?  

The 1k/year tax bill is very appealing and I wouldn’t mind buying in cash to keep this benefit. 

Thank you.