[Avodah] The relevance of the middle perakim of Bava Basra today

[Marty Bluke via Avodah]

Perakim 4-7 of Bava Basra (which Daf Yomi has been learning) deal with the
sale of various things, what is included and what is not. The common
denominator seems to be that these are seemingly solely based on the
accepted business practice during the time of Chazal and what people expect
to get when they consumate a deal. There are few to no Torah based sources
for any of these. Here is a general outline of the perakim.

Perek 4 - Hamocher es habayis discusses what is sold when you sell real
property (houses, bathhouses, courtyards, fields, etc.) and what is not,
for example when you sell a house the Mishna states that you include teh
door but not the key
Perek 5 - Hamocher es hasefina discusses the sale of movable objects, again
detailing what is included in the sale and what is not (boats, wagons,
animals, etc.)
Perek 6 - Hamocher peiros lachaveiro discusses the sale of agricultural
products. It details how much spoilage/wastage there can be in grain and
wine etc. It also discusses selling land to build things on it like a
house, graves, how much land is given, what access etc.
Perek 7 - Deals with sales of real property how exact do the dimensions
need to be.

Given the above, are these at all relevant today? A house buyer in 2017
clearly has very different expectations as to what he is buying in
comparison to the times of Chazal as does someone buying wine, a field, a
boat, etc. The same goes for all of these categories.  Since the mishnayos
seem to be based solely on accepted business practice and have are not
based on pesukim can we simply ignore these today? Am I missing something
here?
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