The reliable way to hire a tradesperson

Hello, We are currently buying a house that has a conservatory attached to it's living room and kitchen. The kitchen has an airtight door between the two but the living room has had the wall removed between it and the conservatory, and there is central heating in the conservatory. There seems to be no building control paperwork for when it was put in but the conservatory has been there since approximately 2007. We are looking to buy the house and open the kitchen into the conservatory, removing the wall between to put an island in (which I imagine will mean putting in a load bearing beam). My question is if the current conservatory/living room would affect this and is there anything we should ask the seller for before purchasing the house (such as retrospective approval) given that there's no paperwork for it. Additionally, we are going to replace the glass in the conservatory. This is all very new to us as we're first time home owners, any feedback would be most appreciated!

Can i build a 1m high double skinned retaining wall, laying standard dense blocks upright (longest side horizontal) for ithe inner skin and standard bricks flat for the outer skin. The wall will be about 5m long.

Hi, we have recently had a bathroom installed and have had a tradesman come in to look at it as we found our shower waste had been left completely unconnected and pouring into our solem. When they were in they also picked out a number of faults including the way our tiles had been fitted as none of them are sitting flush and the tradesman has left grout all over all the tiles. Our toilet is also not bolted down and the cistern was leaking. Should I be concerned and have somebody in to inspect the work