McCrostie began his stock agent career with the National Mortgage Agency (NMA), a mercantile stock and station company in Riverton in 1970.
''I spent 18 months there, then I went to Balclutha.''
Wife June provided his back-up and in addition to looking after their two daughters, she dealt with phone calls and paperwork, and cooked meals for his bosses.
''After Wright Stephenson merged with NMA in 1972, I went to Owaka as a stock agent for them.''
Being a stock agent included extremely early starts, anywhere from 3am to 6am, and late finishes, after the drafting and selling was done.
''I was in Owaka for 10 years and that was a great experience, a great place to live.
''They were great people, with many second generation farmers.
''They had taken over from fathers who had cut and burned the bush to develop the land.''
He remembered attending a cattle sale at Mt Benger saleyards, Roxburgh.
About 1000 cattle were left unsold, so he bought them for $73 each, and a line of transport operators took them to the Owaka pub, where he sold them to local buyers for the same price plus freight.
McCrostie said after 10 years he moved to the stud stock division in Invercargill in 1983.
''Pedigree stock is the number one driver for me.
''Romneys and Herefords were the mainstay in those days and we sold stud stock for big money.''
He dealt with the Chittocks, the Brenssells, the Bains, the Robertsons, the Tripps of Nithdale, the Landels, the Holmeses and many other well-known stud and farming families.
By 2005 he decided to take early retirement from Wrightsons after seeing huge changes in the industry, and in particular the growth of dairying, although he said he ''never really finished working.''
He now works for Carrfields, which took over Elders.
He and June bought a farm, which they sold four years ago and they now live on a lifestyle block near Winton.
When he is not working, he is interested in horse racing and has been on the Riverton Club's management committee for about 20 years.
He also races the odd horse and buys in weanlings to bring them on and then resell.